Peanut Butter Swiss Meringue Buttercream

4 egg whites

3/4 cup sugar

2 teaspoons molasses

20 tablespoons unsalted butter, at cool room temperature

1 teaspoon vanilla extract

1/2 cup (8 tablespoons) peanut butter

Combine the sugar, egg whites and molasses in the stainless steel bowl of an electric mixer.

Bring a large pan of water to simmer, making sure the water is at the same height as the egg whites in the bowl.  Set the bowl in the pan of simmering water and whisk constantly until the mixture reaches 160 degrees on an instant-read thermometer.  (Whisk by hand and cook until the sugar is completely dissolved and the top becomes foamy.  Be careful not to curdle the egg whites; remove from heat if this begins to happen.)

Remove the bowl to the stand mixer and beat on high speed for at least 3 minutes, until the mixture holds glossy, marshmallow-esque peaks and the bowl is completely cool.  Remove two-thirds of the meringue to another bowl.

Switch to the paddle attachment and beat half the butter and one-third of the meringue until well-combined.  Continue to add the remaining two-thirds of the meringue, a dollop at a time.  Add the remaining butter a tablespoon at a time and beat well after each addition.  With the mixer on low, add the vanilla and peanut butter and continue beating for 1 minute to incorporate the additions and reduce air bubbles.

Makes enough to frost a 3-layer 9-inch cake.