One key to a crumbly, tall topping is properly chilling the crumb after mixing and before baking. Though this might produce what looks to be an overly generous amount of crumbs at first, be sure to heap it all on: As the cake rises during baking, the proportions will become just right.
What You Will Need
For the crumb:
- 2 cups all-purpose flour (245 g)
- 1 cup light-brown sugar (200 g)
- 1⁄4 cup natural cane sugar (48 g)
- 2 tsp. ground cinnamon
- 1 tsp. kosher salt
- 1 cup plus 2 Tbsp. (2¼ sticks or 9 oz.) unsalted butter, cut into cubes, then left out to soften slightly
For the cake:
- 2 1⁄4 cups all-purpose flour (275 g)
- 1⁄2 tsp. baking powder
- 1⁄2 tsp. baking soda
- 3⁄4 tsp. kosher salt
- 3⁄4 cup plus 2 Tbsp. (1¾ sticks) unsalted butter, softened, plus more for greasing
- 1 1⁄2 cups natural cane sugar (290 g)
- 3 large eggs
- 2 tsp. pure vanilla extract
- 1 cup full-fat sour cream (215 g)
- Powdered sugar, for garnish
- Make the crumb: In a large bowl, add the flour, both sugars, the cinnamon, and salt; stir. Add the butter; mix it in with your fingers and by squeezing with your palms until it feels saturated and chunky (you will crumble it later), 3–4 minutes. Refrigerate until firm, at least 25 minutes, or until ready to bake the cake.
- Preheat the oven to 350°F and set a rack in the center. Meanwhile, mix the cake: In a large bowl, add the flour, baking powder, baking soda, and salt; stir to combine. In the bowl of a standing mixer fitted with the paddle attachment, beat the butter and sugar at medium-high speed, scraping down the sides of the bowl as needed, until light and fluffy, about 3 minutes. Add the eggs and vanilla, and beat at medium-low speed, scraping down the bowl as needed, until incorporated. With the mixer on low speed, alternate adding the flour mixture (in three batches) and the sour cream (in two batches), beginning and ending with the flour mixture, and beating until just incorporated.
- Grease a 9×13-inch cake pan or baking dish with butter. Add the batter, and use an offset spatula to spread it evenly into a thin layer, filling the corners.
- Retrieve the crumb topping (it should be fully solid). Crumble it evenly over the batter in pebble-size pieces.
- Bake until the cake no longer jiggles when moved, the crumbs are lightly browned, and a cake tester inserted into the center comes out clean, 50–55 minutes. Remove and let cool completely. Dust with powdered sugar to taste, then slice into squares and serve.