Serves 8 to 10.
Recipe adapted from The America's Test Kitchen Family Baking Book
Step 1: Prepare Pan(s); Gather Ingredients
Adjust an oven rack to the lower-middle position and heat the oven to 350 degrees.
1/2 cup (2 1/2 ounces) all-purpose flour
1/2 cup (3 1/2 ounces) packed light brown sugar
2 Tbsp. granulated sugar
1/4 tsp. ground cinnamon
4 Tbsp. (1/2 stick) unsalted butter, softened
1 1/2 cups (7 1/2 ounces) all-purpose flour
1 1/2 tsp. baking powder
10 Tbsp. (1 1/4 sticks) unsalted butter, softened
2/3 cup (4 2/3 ounces) granulated sugar
1/2 tsp. salt
1/2 tsp. grated fresh lemon zest
2 large eggs, room temperature
1 1/2 tsp. vanilla extract (I used 1 tsp. vanilla, then, after separating the batter for the 2 cakes added 1/4 tsp. almond extract to the cherry batter)
4 cups (20 ounces) fresh blueberries (I used 10 oz. blueberries for one cake, 10 oz. sour cherries--slightly less than 2 cups--for the other cake)
I used Ohio locally grown blueberries, but haven't seen any sour cherries this year so I used Trader Joe's jarred Morello cherries. Oregon Fruit Co. canned tart cherries would also work well.
Step 2: Make Streusel Topping
Transfer to a small bowl, and, rinse out mixer bowl if you've used your stand mixer.
Step 3: Make Cake Batter
In a large bowl, beat the butter, sugar, salt, and lemon zest together with an electric mixer on medium speed until light and fluffy, 3 to 6 minutes, scraping down the bowl as necessary (I used my stand mixer).
Beat in the eggs, one at a time, until combined. Beat in the vanilla.
Reduce the mixer speed to low and slowly mix in the flour mixture until just incorporated, about 20 seconds (the batter will be extremely thick and heavy).
If only making one cake, gently fold in the blueberries with a rubber spatula. For my 2 cakes, I separated half the batter into another bowl, mixed 1/4 tsp. almond extract and sour cherries in one bowl, then mixed the blueberries into the remaining batter.
Step 4: Bake
Sprinkle a liberal amount of the streusel evenly over the batter.
Bake the buckle(s) until deep golden brown and a toothpick inserted into the center comes out with a few crumbs attached, about 55 minutes, rotating the pan halfway through baking. (My 6-inch cakes took about 45 minutes to bake.)
Step 5: Enjoy
Buckles can be served many ways, at room temperature, microwaved to warm them a bit, and for dessert, some whipped cream or ice cream compliment the cake beautifully.
Buckles can be held in an airtight container, at room temperature, up to 2 days.