Place in saucepan over med heat; let it melt. Cook until a ring of little bubbles appears around the edge of melted sugar/butter mixture.
Whisk in ½ cup heavy cream. Cook until bubbles reappear. Remove from heat.
Add 1 tsp vanilla.
Pour into mixer bowl. Add 1 ½ cups sifted powdered sugar. Beat at medium speed until combined; add ½ stick butter cut in pieces, beat until smooth and color is lighter. Frosting will still be a little warm.
Place 3/4 cup frosting on top of bottom layer. Add 2nd layer and frost with remaining icing. Do this quickly so it doesn’t set up before you finish spreading.