Everyday Coffee Cake

1. Preheat the oven to 350 degrees F. Grease and flour a large bundt pan very well; set aside.
2. Cream butter and sugars together in a large bowl, until fluffy.
3. Add sour cream (OR plain yogurt plus buttermilk), eggs, and vanilla to the bowl, and stir until well-blended.
4. Dump in the flours, baking powder, baking soda, and nutmeg. Continue mixing until the dry ingredients have fully incorporated, and batter is smooth. Set batter aside while preparing the filling.
5. To make the filling, put the brown sugar and the cinnamon in a small bowl, and mix with a fork to combine.
6. Pour half of the batter into the prepared bundt pan, and smooth with a rubber spatula to level the batter.
7. Sprinkle the filling mixture evenly over the batter in the pan.
8. Cover the filling with the remaining batter, smoothing with a rubber spatula to level the batter. Be sure to smooth the batter to the very edges of the pan, to seal the filling into the cake.
9. Bake at 350ºF for 45–50 minutes, or until a toothpick inserted in the middle of the cake comes out clean.
10. Cool completely in the pan, on a wire rack. The cake should pull away from the sides of the pan as it cools. (If not, gently run a knife along the edges of the pan, after it has cooled.)