Step 1
Preheat oven to 350 degrees F.
Step 2
Whisk together the flour, baking powder, baking soda, and salt in mixing bowl for 30 seconds; reserve. Cream the butter and sugar together until light and fluffy. Beat in the eggs one at a time, mixing thoroughly before adding the next. Beat in sour cream and vanilla. Add the flour mixture, stirring until combined. Stir in walnuts.
Step 3
Butter a 10-inch bundt pan, and dust with flour. Pour half the batter into the pan and spread evenly. Mix the swirl ingredients in a small bowl. Sprinkle around the center of the batter, and cover with the rest of the batter.
Step 4
Bake for 50 minutes, or until a toothpick inserted in the center comes out clean. Let cool 15 minutes before removing from pan.
Step 5
For the glaze: Add the powdered sugar to a mixing bowl, stir in enough milk to create a thick glaze. Stir in the cinnamon to taste. Drizzle over the top of the cake. Once icing is set, slice and serve with hot coffee.