Pre-heat oven to 350 degrees. Grease bundt pan with butter.
Stir together sour cream and baking soda in small bowl or non-metal measuring cup and set aside. (It will begin to foam and rise a bit)
In large mixing bowl, cream together butter and sugar, either by hand or with electric mixer, until sugar dissolves. Beat in eggs and vanilla until smooth and fluffy.
In separate bowl, whisk together flour, salt and baking powder.
Alternate adding the flour mixture and sour cream mixture into large mixing bowl, twice, stirring to incorporate after each addition. Stir just until well combined (do not over mix).
In small bowl, mix together sugars and cinnamon for the swirl.
Pour half of cake batter into bundt plan and smooth the top (it will be thick). Sprinkle half of the sugar swirl mixture over the cake. Add the rest of the batter and smooth the top. Sprinkle batter with remaining sugar mixture.
Bake for 35-40 minutes until cake tester comes out clean (every oven is different so adjust according to your oven). Let rest in bundt pan for 20 minutes, then loosen the edges with a knife and invert cake onto a plate. Serve warm or cool completely.
Enjoy!
