1/3 cup (5-1/3 tablespoons) unsalted butter, softened
1/2 cup (100 grams) granulated sugar
1 large egg, room temperature
1/4 cup (60 grams) sour cream, room temperature
2/3 cup whole milk, room temperature
1 tablespoon vanilla extract
2 cups (256 grams) all-purpose flour
1 tablespoon baking powder
1/8 teaspoon kosher salt
2-1/4 cups (288 grams) all-purpose flour
1-1/4 cups (290 grams) packed light brown sugar
1 tablespoon ground cinnamon
2 sticks unsalted butter, melted (1/2 pound)
Powdered sugar, for dusting (optional but recommended)
- Place a rack in the middle of the oven. Preheat the oven to 350 degrees. Spray a 9×13′ pan with nonstick cooking spray and set aside.
- In a mixer fitted with the paddle attachment, beat the butter and sugar together until light and fluffy, about 2-3 minutes. Add in the egg and sour cream and mix until combined. Scrape down the bowl.
- In a measuring cup or bowl, mix together the milk and vanilla extract. In another bowl, whisk together the flour, baking powder, and salt.
- Turn the mixer on low and alternately add the wet ingredients and the dry ingredients, starting and finishing with the dry ingredients, scraping down the bowl at least once in the middle of mixing and once after the last batch of flour has been mixed in.
- Spread the batter into the prepared pan.
- To make the crumbs – whisk together the flour, brown sugar, and cinnamon until completely combined. Add in the melted butter and stir until the mixture is completely moistened.
- Use your hands to roll pieces of the mixture in your hands until large and small crumbs form, and sprinkle the crumbs over the cake. Continue until the cake is covered in crumbs and is even all over.
- Bake for about 30 minutes, or until the center is firm and springs back when touched. If the cake still isn’t completely cooked, turn down the oven to 325 and bake in 3-5 minute increments until done.
- Remove the cake from the oven and lightly dust with powdered sugar (I normally use a sifter). Let cool, and then dust again with powdered sugar; slice and serve.