Preheat oven to 180°C Spray 2 (23cm) round cake pans with baking spray with flour; line bottom of pans with baking paper.
In the bowl of a stand mixer fitted with the paddle attachment, beat butter and sugar at medium speed until fluffy, 3 to 4 minutes, stopping to scrape sides of bowl. Add eggs, one at a time, beating well after each addition. Beat in vanilla.
In a large bowl, whisk together flour, baking powder, salt, and baking soda. Add flour mixture to butter mixture alternately with buttermilk, beginning and ending with flour mixture, beating until well combined after each addition. Divide batter between prepared pans; using a small offset spatula, smooth tops. Forcefully tap pans on counter several times to evenly spread batter and release air bubbles.
Bake until a wooden pick inserted in center comes out clean, about 35 minutes. Let cool in pans for 10 minutes. Remove from pans, and let cool completely, parchment side down, on wire racks.
Level cake layers, if desired; discard baking paper. Place 1 cake layer on a serving plate. Spoon 2½ cups (about 496 grams) Creamy Vanilla Frosting into a large piping bag fitted with a 1cm round piping tip (Wilton 1A). Pipe frosting evenly over cake layer; smooth with a small offset spatula. Place remaining cake layer on top. Spoon another 2½ cups (about 496 grams) frosting into piping bag. Pipe evenly over top of cake; using a small offset spatula, smooth into an even layer.
Spoon remaining frosting into piping bag. Pipe all over sides of cake; holding a bench scraper or a large offset spatula against sides of cake, scrape off excess frosting until sides are smooth and layers are somewhat exposed. Pile excess frosting on top of cake; using the back of a spoon or a large offset spatula, spread and swirl frosting as desired. Using a bench scraper or a large offset spatula held against sides of cake, scrape frosting one more time to give sides a smooth, finished look.
Creamy Vanilla Frosting
In the bowl of a stand mixer fitted with the paddle attachment, beat butter and salt at medium speed until creamy, about 1 minute, stopping to scrape sides of bowl. With mixer on low speed, gradually add confectioners’ sugar alternately with cream, beginning and ending with confectioners’ sugar, beating just until combined after each addition. Beat in vanilla bean paste. Increase mixer speed to medium; beat until fluffy, about 2 minutes. Use immediately.