Preheat oven to 350°F. Line a standard muffin pan with paper liners or grease with nonstick spray.

With an electric mixer, beat the butter and sugar on high for about 3 minutes until pale and creamy, scraping down the bowl once or twice

Add eggs one at time, mixing after each.

Add vanilla extract and scraped vanilla bean seeds OR vanilla bean paste and mix until incorporated.

In a separate bowl, sift together cake flour, baking powder, baking soda, and salt. Add to the batter in 3 additions, alternating with the buttermilk, ending with the flour mixture. Mix only until flour mixture is incorporated, do not over mix.

Fill cupcake liners 2/3 full and bake until tops spring back when gently pressed and edges are barely turning golden, about 13-15 minutes.

Let cupcakes cool in the pan a few minutes until they are cool enough to touch, then transfer to a wire rack to cool completely.

In the bowl of a stand mixer fitted with a paddle attachment, or in a large bowl with a hand-held mixer, mix all of the ingredients on low speed until it starts to come together.

Increase speed to high and beat for 4-5 minutes until frosting is fluffy, pausing once or twice to scrape the bowl down.

This frosting will be very airy with lots of bubbles. If desired, use a wooden spoon to beat the frosting by hand for 2-3 minutes. This pushes all of the air out of the frosting, leaving it smooth.

Frost cupcakes as desired. I used a pastry bag fitted with an Ateco 849 closed star tip.