Steusel-Top Sour Cream Coffee Cake

Ingredients:

Topping:
1 tablespoon all-purpose flour
1/3 cup firmly packed light brown sugar
1 teaspoon ground cinnamon
2 tablespoons cold unsalted butter, cut into pea-size pieces
3/4 cup chopped walnuts and pecans

Cake:
11/3 cups all-purpose flour
3/4 teaspoon baking powder
1/2 teaspoon baking soda
1/2 teaspoon salt
1/2 cup unsalted butter, at room temperature
1/3 cup granulated sugar
1/4 cup firmly packed light brown sugar
1 egg
1/2 teaspoon pure vanilla extract
1 cup sour cream
Directions:

Preheat the oven to 350°F. Lightly grease an 8-by-8-inch baking pan and set aside.

To make the topping: In a medium bowl, whisk together the flour, brown sugar, and cinnamon until blended. Using your fingers or a pastry blender, work the butter into the flour mixture until the topping is crumbly. Stir in the walnuts and pecans, and set aside.

To make the cake batter: In a medium bowl, whisk together the flour, baking powder, baking soda, and salt until well blended.

In another medium bowl, using a hand mixer set on medium speed, beat the butter until creamy, about 30 seconds. Beat in the granulated and brown sugars until smooth and lump-free. Beat in the egg until well blended, scraping down the sides and bottom of the bowl as necessary. Beat in the vanilla until blended. Add the flour mixture in three parts, alternating with the sour cream, beating until just blended. Scrape down the sides and bottom of the bowl. The batter should be smooth and blended.

Spread the batter into the prepared baking pan and sprinkle the reserved topping over the batter. Bake in the middle of the oven until the cake has risen and browned and a toothpick inserted in the center comes out clean, about 50 minutes. Let the cake cool in the pan for at least 10 minutes. Cut into squares and serve. The coffee cake is best served slightly warm, but it keeps well, wrapped, for 1 to 2 days at room temperature.

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