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"Nerdy Nummies" YouTube star, baker and New York Times best-selling cookbook author Rosanna Pansino shares her incredibly light and airy, yet rich and buttery recipe, which is perfect for topping and filling cakes and cupcakes.

Try it in her Brain Cupcakes for Halloween or anytime, as a topping for her Raspberry Cupcakes made with frozen raspberries.

Adapted from "Baking All Year Round" by Rosanna Pansino. Copyright © 2018 by Rosanna Pansino. Used with permission by Atria Books. All rights reserved.


  • 5 large egg whites
  • 1 cup granulated sugar
  • 1 cup powdered sugar
  • 1/4 teaspoon cream of tartar
  • 1 teaspoon vanilla extract
  • 4 sticks unsalted butter, at room temperature (16 ounces)


Serves: Makes 5 cups


Fill a medium saucepan with 1 inch of water and bring to a simmer.

In a medium heatproof bowl, whisk together the egg whites, granulated sugar, powdered sugar, cream of tartar, and vanilla until combined.

Place the bowl over the simmering water, making sure the bottom of the bowl doesn’t touch the water. Whisk until the mixture is warm and the sugar has dissolved.

Pour the mixture into a stand mixer fitted with the whisk attachment and beat on high speed until the mixture cools to room temperature, 15 to 20 minutes.

On low speed, slowly add the butter 1 tablespoon at a time until fully combined. Scrape down the sides and bottom of the bowl as needed.