Sour Cream Coffee Cake

This is the coffee cake that I have been making all my life. My mother made it,a nd a version of it is in the original Moosewood cookbook, the one I got in the late 1970's and cooked out of throughout my college and medical school career. I had Moosewood before I had Julia Childs. Silly me, I should have had both, but I did not grow up cooking and so I used what I knew. In any case, I have made some variation of this for over 40 years. I put cranberry sauce left over from Thanksgiving in the middle, I use thinly sliced apples there sometimes, and I have always used yogurt, even before it was cool to do so--and I use flavored ones that are going bad with good effect. Cake: 8 tablespoons (113g) unsalted butter, softened 1 cup (198g) sugar 2 large eggs, at room temperature 2 cups (240g) King Arthur Unbleached All-Purpose Flour 1 teaspoon baking powder 1/4 teaspoon baking soda 1/2 teaspoon salt 1 cup (227g) sour cream or yogurt, at room temperature Topping: 1/2 cup (99g) sugar 2 teaspoons cinnamon 2 teaspoons vanilla extract 1/2 cup (57g) chopped walnuts or pecans, optional Preheat the oven to 350°F. Grease and flour a 9 1/2" tube pan, or a 9" x 9" pan. To make the cake: Beat together the butter, sugar, and eggs. In a separate bowl, mix together the flour, baking powder, baking soda, and salt. Add the flour mixture to the butter mixture alternately with the sour cream or yogurt, stirring after each addition. To make the topping: Combine all of the topping ingredients, stirring until evenly crumbly. Spread half the batter in the pan, and sprinkle with half the topping mixture. Repeat with the remaining batter and topping. Bake the coffeecake for 30 to 40 minutes, or until a toothpick inserted into the center comes out clean, or with just a few moist crumbs sticking to it. Glass pans may take an additional 5 to 10 minutes to bake through completely. Remove the cake from the oven; if you've baked it in a tube pan, wait 10 minutes, loosen the edges, and carefully turn it out of the pan. Place the cake right-side up (topping up) on a plate to serve. If you've baked the cake in a 9" x 9" pan, just serve it right from the pan. Serve the cake warm or at room temperature. Wrap the completely cooled cake airtight, and store at room temperature for several days; freeze for longer storage.