Cinnamon-Streusel Coffee Cake

STREUSEL TOPPING

 * 1 cup granulated sugar
 * 1/4 teaspoon salt (if you use unsalted butter)
 * 1 cup King Arthur Unbleached All-Purpose Flour
 * 1 tablespoon ground cinnamon
 * 6 tablespoons butter, melted

FILLING

 * 1 cup brown sugar, light or dark
 * 1 1/2 tablespoons ground cinnamon
 * 1 teaspoon unsweetened cocoa powder

CAKE

 * 3/4 cup butter
 * 1 teaspoon salt (1 ¼ teaspoons if you use unsalted butter)
 * 1 1/2 cups granulated sugar
 * 1/3 cup brown sugar
 * 2 1/2 teaspoons baking powder
 * 2 teaspoons vanilla extract
 * 3 large eggs
 * 3/4 cup sour cream or plain yogurt
 * 1 1/4 cups milk (anything from skim to whole)
 * 3 3/4 cups King Arthur Unbleached All-Purpose Flour

Instructions

 * 1) Preheat the oven to 350°F. Lightly grease a 9" x 13" pan, or two 9" round cake pans.
 * 2) Make the topping by whisking together the sugar, salt, flour, and cinnamon. Add the melted butter, stirring until well combined. Set the topping aside.
 * 3) Make the filling by mixing together the brown sugar, cinnamon, and cocoa powder. Note that the cocoa powder is used strictly for color, not flavor; leave it out if you like. Set it aside.
 * 4) To make the cake, in a large bowl, beat together the butter, salt, sugars, baking powder, and vanilla until well combined and smooth.
 * 5) Add the eggs one at a time, beating well after each addition.
 * 6) In a separate bowl, whisk together the sour cream or yogurt and milk till well combined. You don't need to whisk out all the lumps.
 * 7) Add the flour to the butter mixture alternately with the milk/sour cream mixture, beating gently to combine.
 * 8) Pour/spread half the batter (a scant 3 cups) into the prepared pan(s), spreading all the way to the edges. If you're using two 9" round pans, spread 1 1/3 cups batter in each pan.
 * 9) Sprinkle the filling evenly on the batter.
 * 10) Spread the remaining batter atop the filling. Use a table knife to gently swirl the filling into the batter, as though you were making a marble cake. Don't combine filling and batter thoroughly; just swirl the filling through the batter.
 * 11) Sprinkle the topping over the batter in the pan.
 * 12) Bake the cake until it's a dark golden brown around the edges; medium-golden with no light patches showing on top, and a toothpick or cake tester inserted into the center comes out clean, about 55 to 60 minutes for the 9" x 13" pan, 50 to 55 minutes for the 9" round pans. When pressed gently in the middle, the cake should spring back.
 * 13) Remove the cake from the oven and allow it to cool for 20 minutes before cutting and serving. Serve cake right from the pan.