The Ultimate Brown Butter Plum Crumble Bars
Why You’ll Love This Recipe
I have a deep love for stone fruit desserts, but I often find them too sweet or too wet. The filling can make the bottom crust soggy, which ruins the whole experience. That is why I became obsessed with creating a bar that keeps its structure while bursting with plum flavor. These Brown Butter Plum Crumble Bars are the result of that obsession.
The secret is all in the brown butter. When you cook butter until it turns a deep amber color, it releases a nutty, toasty aroma that plain butter simply cannot match. This nuttiness pairs perfectly with the tartness of plums. The first time I made these, my kitchen smelled like a high-end bakery. I knew I had cracked the code. I also learned a trick from reading about the science of browning butter on Wikipedia that helped me avoid burning it. This one change took these bars from good to absolutely incredible.
Ingredients
- 1 cup unsalted butter
- 2 cups all-purpose flour
- 1/2 cup granulated sugar
- 1/4 cup packed brown sugar
- 1/2 teaspoon salt
- 1/2 teaspoon cinnamon
- 1 large egg yolk
- 1 teaspoon vanilla extract
- 4 cups plums, pitted and sliced (about 6-7 medium plums)
- 1/4 cup granulated sugar (for filling)
- 2 tablespoons cornstarch
- 1 tablespoon lemon juice
- 1/4 cup rolled oats (for topping)
- 1/4 cup chopped pecans (for topping)
Step-by-Step Directions
- Start by browning the butter. Place the butter in a light-colored saucepan over medium heat. Swirl the pan occasionally. You will see it foam up, then the foam will subside. Watch closely for tiny brown specks to appear at the bottom. The moment the butter smells nutty and turns a rich amber, pull it off the heat. Pour it into a heatproof bowl to stop the cooking. Let it cool for 10 minutes.
- While the butter cools, mix the dry ingredients for the crust. In a large bowl, whisk together the flour, 1/2 cup of granulated sugar, the brown sugar, salt, and cinnamon.
- Pour the cooled brown butter into the flour mixture. Add the egg yolk and vanilla. Stir with a fork until the dough looks like coarse crumbs and holds together when you squeeze it. Do not overmix.
- Press about two-thirds of this dough firmly into the bottom of a 9×13 inch baking pan lined with parchment paper. Make sure the layer is even. Put the pan and the remaining dough in the refrigerator for 20 minutes. This chill time is crucial for a flaky crust.
- While the crust chills, make the filling. Toss the sliced plums with 1/4 cup of granulated sugar, the cornstarch, and the lemon juice. The mixture will look a bit cloudy at first. Let it sit for 5 minutes so the juices start to release.
- Preheat your oven to 375 degrees F.
- Take the pan out of the fridge. Spread the plum mixture evenly over the chilled crust. It will look like a lot of fruit, but it bakes down beautifully.
- Take the reserved dough out of the fridge. Mix in the rolled oats and chopped pecans with your fingers until combined. Sprinkle this crumbly mixture over the plums. Do not press it down. You want clumps of topping.
- Bake for 40 to 45 minutes. The top should be a deep golden brown and the plum filling should be bubbling around the edges. Your whole house will smell like warm fruit and brown butter. Let the bars cool completely in the pan on a wire rack. This is the hardest part, but it is necessary. If you cut them while warm, the filling will run everywhere.
Pro Tips for Success
The most common mistake I see when people make bars like these is not browning the butter correctly. You must use a light-colored pan so you can actually see the color change. If you use a dark nonstick pan, you will likely burn the butter before you even see the specks. For a deeper dive into how browning changes the flavor of baked goods, you can read about the Maillard reaction on Wikipedia. It is the same chemical process that makes a steak taste amazing.
Another big tip is to not skip chilling the crust. A warm crust will spread and soak up the plum juices before it has a chance to set. Chilling it firms up the butter, which creates steam pockets in the oven. These steam pockets make the crust flaky instead of dense.
Finally, be patient with the cooling time. I know it is tempting to dig in right away. But these Brown Butter Plum Crumble Bars need at least two hours to fully set. If you cut them too early, you will end up with a delicious but messy plum soup.
Servings and Timing
This recipe makes 12 generous bars. The total active time is about 25 minutes, plus 20 minutes of chilling and 45 minutes of baking. You will need at least 2 hours of cooling time after baking, so plan to make them in the morning if you want to serve them in the afternoon.
Variations and Substitutions
If you do not have plums, you can use nectarines or apricots. Just keep the total amount the same. For a gluten-free version, swap the all-purpose flour for a 1-to-1 gluten-free baking blend and use certified gluten-free oats. You can also leave out the pecans if you have a nut allergy. Just add an extra tablespoon of oats to the topping instead.
If you want a more intense brown butter flavor, you can brown the butter and then refrigerate it until it is solid again. Then cream it with the sugars. This takes more time but creates an even nuttier crust. I have tried this method and it is wonderful for a special occasion.
What to Serve With This
These bars are fantastic on their own, but they become a real showstopper with a scoop of vanilla bean ice cream. The cold creaminess balances the warm, jammy plum filling perfectly. If you want to round out a summer dessert table, I highly recommend serving them alongside my [LINK: Brown Butter Peach Crumble Bars]peach crumble bars[/LINK] for a stone fruit double feature.
For a brunch spread, these bars pair beautifully with a cup of strong coffee. They also go great with [LINK: 5 Ingredient Raspberry Shortbread Bars]these simple raspberry shortbread bars[/LINK] if you want a variety of flavors. The tartness of the raspberry and the nuttiness of the brown butter plum are a fantastic contrast.
Storage and Reheating
Store leftover Brown Butter Plum Crumble Bars in an airtight container at room temperature for up to 3 days. If you stack them, place a sheet of parchment paper between the layers to prevent the crumble topping from sticking. For longer storage, you can refrigerate them for up to a week. The crust will firm up in the fridge, which some people actually prefer.
To reheat a single bar, place it on a baking sheet in a 300 degree F oven for 5 to 7 minutes. This will warm the filling and crisp up the topping again. I do not recommend microwaving them, as the topping will become soft and the crust will turn chewy.
FAQs
Q: Can I use frozen plums instead of fresh ones?
You can, but you need to thaw them completely first and drain off any excess liquid. Frozen plums release much more water than fresh ones. If you skip this step, your filling will be too runny and could make the crust soggy. I also recommend adding an extra teaspoon of cornstarch to help thicken the juices.
Q: What happens if my brown butter gets too dark and smells burnt?
You have to start over. Burnt brown butter has a bitter, acrid taste that will ruin the entire crust. There is no way to fix it. The key is to keep a close eye on it. Once you see the brown specks, remove it from the heat immediately. If you are nervous, you can pull it off the heat just before you think it is done, because the residual heat in the pan will continue to cook it for a few seconds.
Q: My plums are very tart. Should I add more sugar to the filling?
Absolutely. The tartness of plums can vary wildly depending on the variety and ripeness. If your plums are making your mouth pucker, increase the sugar in the filling by one to two tablespoons. Taste a slice of the raw plum after you toss it with the sugar. It should taste pleasantly sweet with a hint of tartness, not sour.
Q: Can I make these Brown Butter Plum Crumble Bars in a glass baking dish?
You can, but you need to reduce the oven temperature by 25 degrees F. Glass heats up more slowly than metal but retains heat much longer. If you bake at the full temperature, the bottom crust can burn before the top is done. I prefer a metal pan for these bars because it gives a more even, golden crust.
Q: Why did my crumble topping sink into the plum filling?
This usually happens if the filling is too wet or if you pressed the topping down. The topping needs to sit loosely on top of the plums. If the plums released too much juice, the topping can absorb it and sink. To prevent this, make sure your plums are not overripe and that you use the full amount of cornstarch. You can also try baking the bars on the lower rack of the oven to help the bottom crust set faster.
Conclusion
I hope you give these Brown Butter Plum Crumble Bars a try soon. They are the perfect way to use up a bounty of summer plums. The nutty brown butter, the jammy fruit, and the crunchy oat topping make a combination that is hard to beat. Let me know how they turn out for you in the comments.
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