Using a paddle, cream together sugar and butter until pale in color and fluffy (measure other ingredients during this time). Scrape down sides of bowl.
Add in eggs and vanilla paste in three parts until thoroughly combined, and scrape down the sides during each addition.
Next combine all dry ingredients and whisk together.
Add half of the dry ingredients and sour cream to the butter mixture. Scrape down sides of the bowl and add the rest. Mix until combined.
Split final batter into three separate containers and mix in the respective flavorings into each container.