This is the classic frosting that goes on a cake as the crumb coat.
It is thick and creamy and very sweet. A little goes a long way.
This makes enough for a thin crumb coating on an 8" 2 layer cake.
Source:
https://www.allrecipes.com/recipe/174347/quick-and-almost-professional-buttercream-icing/
½ cup unsalted butter, at room temperature
2 cups confectioners' sugar, sifted
1 ½ teaspoons pure vanilla extract
2 tablespoons milk
3 drops food coloring, or as needed (Optional)
Cream butter in the bowl of a stand mixer fitted with the paddle attachment until smooth and fluffy.
Gradually beat in confectioners' sugar until fully incorporated.
Beat in vanilla extract.
Add milk and beat for an additional 3 to 4 minutes.
Add food coloring, if using, and beat for thirty seconds until smooth or until desired color is reached.
Use immediately or store buttercream in an airtight container at room temperature for up to three days.