Heat oven to 350°F first.
Grease bundt pan with butter well.
Mix brown sugar and cinnamon together.
Add melted butter to cinnamon mix.
Beat butter and sugar until light.
Add eggs one by one.
Mix in vanilla and sour cream.
Mix flour, baking powder, soda, salt.
Add dry stuff to wet stuff.
Pour in milk and mix gently.
Pour half batter into pan.
Sprinkle cinnamon mix over batter evenly.
Add rest of batter on top.
Bake for 50-55 minutes until done.
Cool in pan for 15 minutes.
Turn out onto wire rack.