Preheat oven to 350 degrees.

In a large bowl cream together sugar and butter.

Add in eggs and vanilla and beat.

Gently fold in sour cream.

In a separate bowl mix together flour and baking powder.

Blend into batter by hand. The batter will be thick.

In a small bowl mix together cinnamon and brown sugar.

Pour half of the batter into a well greased and flour bunt pan.

Sprinkle 3/4 of cinnamon mixture over batter.

Spread remaining batter over filling.

Top with the rest of the cinnamon mixture.

Bake for 45-60 minutes (until center comes out clean when you insert a toothpick).

Once removed from oven immediately run a knife round the outside and inside edges.

Cool 15 minutes in pan then invert on to plate to cool completely.