Basic Buttercream

Again, thanks to Martha Stewart.

12 oz unsalted butter, softened
1 lb. powdered sugar
1/2 tsp. vanilla

Beat butter with a mixer on medium-high speed until pale and creamy, about 2 min. Reduce speed to medium. Add sugar, 1/2 cup at a time, beating after each addition, about 5 min. (After every 2 additions, increase speed to high, and beat for 10 seconds, then reduce speed to medium high.) Add vanilla, and beat until buttercream is smooth. Use immediately, or cover and refrigerate for up to 3 days. Bring to room temperature, and beat on low speed until smooth before using.

Cream cheese frosting

For spice cakes and carrot cakes and whatever else you want.
8 oz. cream cheese, at room temperature
4 Tbsp. butter
2 cups powdered sugar
1 tsp. vanilla extract

Combine ingredients in a mix bowl and beat until perfectly smooth and spreadable. Enough to fill and frost an 8- inch two-layer cake.