1tspcoarse Kosher salt(if using table salt, use half the amount)
½cupfull-fat sour cream
1 ½cupsunsalted butter,softened to room temperature
¼tspcoarse Kosher salt(if using table salt, use half the amount)
1 ½tspvanilla extract
2-3tbspmilk or cream,if needed
Preheat the oven to 350 F. Line two standard-sized muffin pans with 24 paper liners.
In the bowl of your stand mixer fitted with the paddle attachment, beat the butter and sugar on medium speed for 4 minutes, scraping the bowl down several times.
Add the eggs, one at a time, beating each for 15 seconds before adding the next. Scrape the bowl down, add the vanilla, and beat again. If the mixture looks lumpy, don't worry, it will smooth out in the end.
In a separate bowl, sift together the cake flour, baking powder and salt.
With the mixer on low, add 1/3 of the flour mixture, then add the sour cream. Add another 1/3 of the flour mixture, then add the buttermilk. Add the remaining 1/3 of the flour mixture. Increase speed to medium and beat for 30 seconds, until the batter is smooth and thick.
Use a cupcake scoop / ice cream scoop to evenly measure the batter into the paper liners. One level scoop is enough batter for each; if you overfill the cups, the batter will spill over the edges and you'll get muffin tops with browned edges instead of gently domed cupcakes.
Bake the cupcakes on the center oven rack for about 20 minutes, until the centers of the cupcakes spring back when gently touched.
Cool the cupcakes in the pans for 5 minutes, then carefully transfer to a wire rack to cool completely before frosting.
In the bowl of your stand mixer fitted with the whisk attachment, beat the butter for 1 minute until smooth.
In a separate bowl, combine the powdered sugar, meringue powder and salt. With the mixer running on low, add the powdered sugar mixture by spoonfuls to the butter, mixing just until combined. The buttercream will be clumpy at this point.
Add the vanilla, and increase the speed to medium. Whip the buttercream for about 5 minutes, scraping the bowl several times, until very light and fluffy, adding the milk as needed for desired consistency.
Spread or pipe the buttercream onto the cooled cupcakes.
These can be baked and frosted one day in advance, stored in the refrigerator in an airtight container. Bring to room temperature before serving.