This Blackberry Crumb Cake will “delight picnic-goers with a portable version of summer berry crumble: a perfect marriage of tart fruit and tender cake, capped with a slightly crunchy topping.” Martha Stewart
While you prepare the cake, refrigerate the crumb topping. This will help give it a nubbly texture once baked.
To store the cake, keep in an airtight container at room temperature, up to 3 days.
- 6 tablespoon unsalted butter melted
- 8 tablespoon unsalted butter room temperature
- 1 3/4 cup all-purpose flour (spooned and leveled) divided, plus more for pan
- ½ cup light-brown sugar packed
- ½ teaspoon kosher salt
- ½ teaspoon baking powder
- 1 cup confectioners’ sugar
- ½ teaspoon vanilla extract
- 2 large eggs
- 10 ounce fresh blackberries (about 2 containers)
Set the oven rack in the center position. Preheat oven to 350 degrees. Butter an 8‑inch square baking pan. Line bottom with parchment paper, leaving an overhang on two sides; butter and flour paper, tapping out excess.
Make topping: In a medium bowl, whisk together melted butter, brown sugar, and ¼ teaspoon salt; add 1 cup flour, and mix with a fork until large moist crumbs form. Refrigerate topping until ready to use.
In a medium bowl, whisk together remaining 3/4 cup flour, baking powder, and remaining ¼ teaspoon salt; set aside. In a large bowl, using an electric mixer, beat room-temperature butter, confectioners’ sugar, and vanilla until light and fluffy; add eggs, one at a time, beating well after each addition. Reduce speed to low; mix in flour mixture. Spread batter evenly in pan; sprinkle with blackberries, then chilled topping.
Bake until golden and a toothpick inserted in center comes out with moist crumbs attached, 45 to 50 minutes. Cool completely in pan. Using paper overhang, lift cake onto a work surface; cut into 16 squares.