In a small saucepan over medium heat, whisk flour into milk and heat until it thickens (stir constantly). Remove from heat, stir in vanilla and salt and let the mixture cool to room temp. This is important because if you don’t let it cool, the end result will be lumpy and will separate.
Cream the butter (or butter substitute) and sugar together with an electric mixer. Add cooled milk/flour mixture and beat until it resembles whipped cream.
for Chocolate Frosting
Add 4 tablespoons cocoa and 5 tablespoons sugar to the beating process after the butter and sugar are creamed together and beat to combine. Then proceed with the milk/flour process as described above. For extra chocolate flavor, reduce the vanilla extract to 1 1/2 teaspoons and add 1/2 teaspoon gluten-free chocolate extract at the prescribed time.