Preheat oven to 350 F (175 C).

Add granulated sugar and vanilla bean to the bowl of a stand mixer, and beat on medium speed for about 30 seconds until blended. Add in the cake flour, baking powder, baking soda and salt, and beat for an additional 1 minutes until well-mixed. Add butter and mix on medium-low speed for about 2 minutes until well combined and a little crumbly.

In a separate small mixing bowl, whisk together eggs, Greek yogurt (or sour cream), and vanilla extract until smooth. Add the egg mixture to the flour mixture and beat on medium speed until just combined.

Slowly add milk and mix on low speed until just combined. The batter will be very thin and liquid.

Fill cupcake liners just over 1/2 full. Bake for 14 minutes and then test to see if they are done. They are done when a toothpick comes out without wet batter stuck to it. Remove and let cool on a cooling rack. Once the cupcakes have reached room temperature, frost with the Vanilla Buttercream Frosting (recipe below).

Add the butter to the bowl of a stand mixer and beat for 1 minute on medium speed until smooth. Add the powdered sugar, salt, vanilla extract, the seeds of a vanilla bean and about 2 Tbsp. milk and reduce speed to low. Beat for a minute or so until the sugar no longer sprays. Then increase speed to medium high and beat for an additional minute until smooth. Add an extra tablespoon or two of the milk if you need a thinner frosting.