In a large mixing bowl, cream the butter until fully mixed.
Sift 1 cup of the powdered sugar into the butter mix and mix until fully incorporated.
Sift another cup of powdered sugar into the bowl and mix again. Mixture will be crumbly, but keep mixing.
Once all sugar is incorporated, add vanilla extract and 2 Tablespoons milk. Mix.
Check consistency and if needed, add another Tbsp. of milk and mix again.
Use as desired.
Notes
Use a deep bowl to prevent powdered sugar from dusting up over the bowl. Use a paper towel to block any remaining powdered sugar.
For thinner consistency, add more milk. A bit thicker, use less.
Food coloring can be added to create different colors, however, it can make the frosting too thin. Look for coloring that is gel-based like Wilton food coloring.
For a cinnamon buttercream, add 1 teaspoon ground cinnamon after adding the vanilla and milk.