Preheat oven to 350°. Spray 2 (9-inch) cake pans with baking spray with flour and line bottoms with parchment paper.
In the bowl of a stand mixer fitted with the paddle attachment, whisk together flour, sugar, baking powder, baking soda, and kosher salt. Add butter and beat at a medium-low speed until butter is incorporated and mixture resembles coarse meal, about 2 minutes.
In a medium bowl, whisk together milk, egg whites, and vanilla bean paste. With mixer at low speed, add one-third of milk mixture, approximately ⅔ cup, to flour mixture. Increase mixer speed to medium and beat until light and fluffy, 1 to 2 minutes. With mixer at low speed, gradually add the rest of the milk mixture, beating until combined, stopping occasionally to scrape down sides of bowl. Beat until combined. Divide batter evenly between prepared pans.
Bake until a wooden pick inserted in centers comes out clean, 20 to 30 minutes. Let cool in pans for 10 minutes before moving to a wire rack; let cool completely. Level cooled cake layers, if desired. Place one layer on a serving plate. Spread 1½ cups Vanilla Buttercream in an even layer, and top with remaining cake layer. Spread a thin layer of buttercream over top and sides of cake, scraping away any excess. Refrigerate just until chilled, about 15 minutes.
Spread remaining buttercream over top and sides of chilled cake.
On a work surface lightly dusted with confectioners’ sugar, roll fondant out to a 16-inch circle, approximately ⅛-inch thick. Carefully drape fondant over lightly chilled cake, smoothing from the top to the sides to smooth out any air bubbles and fully adhere fondant to cake. Trim base of cake to discard any excess fondant.
Recipe by Victoria at https://victoriamag.com/snowflake-cake-with-vanilla-buttercream/