1. Preheat oven to 325°F (163°C). Grease and flour a 10-inch bundt pan or 9×5-inch loaf pan.

2. In a large mixing bowl beat butter and sugar until light and fluffy, about 4 minutes.

3. Add eggs one at a time, beating well after each addition. Mix in vanilla extract.

4. In a separate bowl whisk together flour, baking powder, and salt.

5. Gradually add dry ingredients to the butter mixture alternating with sour cream. Mix until just combined.

6. In a small bowl combine brown sugar, cinnamon, and melted butter to make the cinnamon swirl mixture.

7. Spread half of the cake batter into the prepared pan.

8. Sprinkle half of the cinnamon mixture over the batter.

9. Add remaining batter and top with the remaining cinnamon mixture.

10. Use a knife to gently swirl the cinnamon mixture through the batter.

11. Bake for 60 to 70 minutes or until a toothpick inserted into the center comes out clean.

12. Cool in the pan for 15 minutes, then transfer to a wire rack to cool completely.

13. Whisk together powdered sugar, milk, and vanilla. Drizzle glaze over the cooled cake before serving.