Step 1

Combine sugar, flour, and salt in a medium saucepan and whisk until well combined.

Step 2

Add milk and whisk together until mixture is well combined.

Step 3

Heat mixture over medium heat, stirring constantly, until the mixture is thick and pudding-like. Do not heat over high heat or the mixture will cook too quickly and the sugar won’t properly dissolve. Remove from heat.

Step 4

Pour into a bowl and cover with plastic wrap pressed directly on top to prevent a skin from forming. Allow to cool completely to room temperature or refrigerate for a day or two before using. If refrigerating ahead of time, bring back to room temperature before proceeding.

Step 5

Once cooled, add the butter to a mixing bowl and beat on high speed until light and fluffy, about 3 minutes.

Step 6

Add the flour mixture (at room temperature) one tablespoon at a time, mixing on medium speed until well combined before adding the next.

Step 7

Add the vanilla extract and mix until well combined.

Step 8

Whip the frosting on medium-high speed until light and fluffy, 2-3 minutes.

Step 9

Use immediately or store in the fridge for up to a week or freeze for up to 3 months. Allow buttercream to come back to room temperature before using.