Easy Buttercream for Sunflower Cupcake Cake

Beat butter and vanilla with a mixer on medium-high speed until pale and fluffy, about 2 minutes. Reduce speed to low. Add sugar, 1 cup at a time, beating well after each addition. Raise speed to high, and beat until well combined, 10 to 20 seconds more. Transfer to a bowl, and cover with plastic wrap until ready to use.