1 cup unsalted butter, at room temperature
4 cups icing sugar
6 tbsp 35% cream
Beat 1 cup butter in a large bowl, using an electric mixer, until creamy, 1 min. Gradually add the icing sugar. (It's okay if it looks dry!) Beat in the 35% cream until fluffy and smooth, 1to 2 min.
Vanilla: Beat in 2 tsp vanilla extract.
Chocolate: Beat in 8oz melted, unsweetened chocolate.
Berry: Beat in 3 tbsp strawberry, raspberry or blueberry jam. Taste, then beat in more jam, if desired.
Lemon: Beat in 1/2 tsp lemon extract and 2 tbsp freshly squeezed lemon juice. If the buttercream gets a little runny, beat in more icing sugar until fluffy.