New York-Style Crumb Cake with Blueberry Jam

From Martha Stewart

European immigrants made this confection -- which has large, crisp crumbs on top -- a New York City coffee-shop favorite. An optional layer of jam between the batter and topping adds a fruity component.

Serves 10 to 12

Ingredients
For the crumb topping:
    3 1/2 cups cake flour (not self-rising)
    2/3 cup granulated sugar
    2/3 cup packed dark-brown sugar
    1 1/2 teaspoons ground cinnamon
    Coarse salt
    2 1/2 sticks unsalted butter, melted
   
For the cake:
    1 1/2 sticks unsalted butter, room temperature, plus more for pan
    2 1/2 cups cake flour (not self-rising)
    1/2 teaspoon baking soda
    Coarse salt
    1 cup granulated sugar
    2 large eggs plus 2 large egg yolks
    1 teaspoon pure vanilla extract
    2/3 cup low-fat buttermilk
    1 cup store-bought blueberry jam (optional)
    Confectioners' sugar, for dusting

Method
Make the crumb topping: Mix together flour, sugars, cinnamon, and 1/2 teaspoon salt in a medium bowl. Pour warm melted butter over mixture, and mix using your hands until medium to large clumps form.
   
Preheat oven to 325°F. Make the cake: Butter a 9-by-13-inch baking pan. Whisk together flour, baking soda, and 1/2 teaspoon salt in a medium bowl.
   
Beat butter and granulated sugar with a mixer on medium speed until pale and fluffy, about 2 minutes. Beat in eggs and yolks, 1 at a time, then vanilla. Beat in flour mixture in 3 additions, alternating with buttermilk, beginning and ending with flour. Continue to beat until well combined.
   
Spoon batter into pan, and spread evenly using an offset spatula. Spread with jam, if using. Sprinkle crumb-topping mixture evenly over top.
   
Bake until golden brown and a toothpick inserted into the center comes out clean, about 1 hour. Transfer pan to a wire rack. Let cake cool slightly, about 15 minutes. Dust with confectioners' sugar. Serve warm or at room temperature.

Cook's Note
Coffee cake can be stored at room temperature for up to 5 days.