Make a buttery crumb cake with a lightly spiced topping

By America’S Test Kitchen The Associated Press

The essence of crumb cake is the balance between the buttery cake and the thick, lightly spiced topping.
Starting with our favourite yellow cake recipe, we realized we needed to reduce the amount of butter or the richness would be overwhelming. We also wanted our crumb topping to be soft and cookie-like, not a crunchy streusel.
Don’t be tempted to substitute all-purpose flour for the cake flour, as doing so will make a dry, tough cake. If you don’t have buttermilk, you can substitute an equal amount of plain low-fat yogurt.
Take care to not push the crumbs into the batter. This recipe can be doubled and baked in a 13-by-9-inch pan. If doubling, increase the baking time to about 45 minutes. We did not like the result when we froze this cake.
Servings: 8-10
Start to finish: 1 hour, 15 minutes (Active time: 30 minutes)
Crumb Topping:8 tablespoons unsalted butter, melted
1/3 cup (2 1/3 ounces) granulated sugar
1/3 cup packed (2 1/3 ounces) dark brown sugar
3/4 teaspoon ground cinnamon
1/8 teaspoon salt
1 3/4 cups (7 ounces) cake flour
Cake:1 1/4 cups (5 ounces) cake flour
1/2 cup (3 1/2 ounces) granulated sugar
1/4 teaspoon baking soda
1/4 teaspoon salt
6 tablespoons unsalted butter, cut into 6 pieces and softened
1/3 cup buttermilk
1 large egg plus 1 large yolk
1 teaspoon vanilla extract
Confectioners’ sugar
Adjust oven rack to upper-middle position and heat oven to 325 F. Cut 16-inch length of parchment paper (or aluminum foil) and fold lengthwise to 7-inch width. Spray 8-inch square baking pan with vegetable oil spray and fit parchment into pan, pushing it up sides; allow excess to hang over edges of pan.
For the crumb topping Whisk melted butter, granulated sugar, brown sugar, cinnamon, and salt together in medium bowl to combine. Add flour and stir with rubber spatula or wooden spoon until mixture resembles thick, cohesive dough; set aside to cool to room temperature, 10 to 15 minutes.
For the cake Using stand mixer fitted with paddle, mix flour, granulated sugar, baking soda, and salt on low speed to combine. With mixer running, add softened butter 1 piece at a time. Continue beating until mixture resembles moist crumbs, with no visible butter chunks remaining, 1 to 2 minutes. Add buttermilk, egg and yolk, and vanilla and beat on medium-high speed until light and fluffy, about 1 minute, scraping down bowl as needed.
Transfer batter to prepared pan. Using rubber spatula, spread batter into even layer. Break apart crumb topping into large pea-size pieces and spread in even layer over batter, beginning with edges and then working toward centre.
Bake until crumbs are golden and toothpick inserted in centre of cake comes out clean, 35 to 40 minutes, rotating pan halfway through baking. Let cool on wire rack for at least 30 minutes. Remove cake from pan by lifting parchment overhang. Dust with confectioners’ sugar just before serving.