Sour Cream Coffee Cake

1/2 cup butter

3/4 cup sugar

1 egg

1/2 cup sour cream

1/2 tsp vanilla extract

1 cup flour

1/2 tsp baking powder

1/2 tsp baking soda

1/4 tsp salt

FILLING:

2 Tbsp brown sugar

1/2 cup chopped nuts

1/2 tsp cinnamon

Cream butter and sugar until very light and fluffy (high speed on mixer).
Beat in egg (high speed on mixer).
Fold into the mixture the sour cream and vanilla (low speed just till blended).
Sift together in another bowl the flour, baking powder, baking soda and salt.
Fold into the mixture until blended (low speed, very gently, just till moistened).
In another bowl, combine the Filling (brown sugar, nuts, cinnamon) ingredients.
Fill paper cups 1/2 full with batter; top with 1 tsp of Filling; fill the cup with more batter to make it about two-thirds full; top with 1 tsp of Filling.
Bake 20 minutes or until a toothpick inserted in center comes out clean.
Remove immediately from the muffin tin.