Ingredients
1egg
1cupwhite sugar
½cupmilk
1⅓cupsunsalted butter,at room temperature
1tbsprum
1tspvanilla extract
Preparation
Beat egg with a fork in a small, heavy saucepan.
Mix in sugar and milk.
Heat on medium-low heat, whisking constantly, until it just starts to boil.
Continue beating rapidly until mixture thickens to a thin custard consistency.
Remove from heat and cool completely, about 1 hour.
Beat butter in a bowl with an electric mixer until light and creamy, about 5 minutes.
Add cooled custard, 1 to 2 tablespoons at a time, beating well after each addition.
Beat in rum and vanilla extract.
Keep beating until buttercream is very light and fluffy.
