This is a recipe from a book called Holiday Baking, New and Traditional Recipes for Wintertime Holidays by Sara Perry.
I was trying to make the "Streusel-Top Sour Cream Coffee Cake" but you can see from the picture that the streusel topping sort of melted into the cake. Also I had no sour cream and used low-fat vanilla yogurt instead. It didn't turn out exactly like the picture in the book but it was easy to make and very tasty. I think what happened with the streusel was my butter was too warm.
Anyway, here's the recipe. Enjoy!
Streusel-Top Sour Cream Coffee Cake
1 T all-purpose flour
1/3 C firmly packed light brown sugar
1 t ground cinnamon
2 T cold unsalted butter, cut into pea-size pieces
3/4 C chopped walnuts and pecans
1 1/3 C all-purpose flour
3/4 t baking powder
1/2 t baking soda
1/2 t salt
6 T unsalted butter, at room temperature
1/3 C granulated sugar
1/4 C firmly packed light brown sugar
3/4 t pure vanilla extract
3/4 C sour cream
1. Preheat the oven to 350°. Grease an 8" x 8" baking pan lightly and set aside.
2. 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.
3. TO MAKE THE CAKE BATTER: In a medium bowl, whisk together the flour, baking powder, baking soda, and salt until well blended.
4. 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 thick batter should be smooth and blended.
5. 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 begins to pull away from the sides and toothpick inserted in the center comes out clean, about 35 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 or 2 days at room termperature.