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Swiss Meringue Buttercream

This recipe will make about 4 cups of buttercream, enough for a 6-inch, three-layer cake.

Prep Time
30 mins
Cook Time
30 mins
Course: Dessert
Cuisine: American

Ingredients

  • 4 large egg whites
  • 1 ⅓ cups granulated sugar
  • pinch fine sea salt
  • 22 tablespoons (2 ¾ sticks) unsalted butter at room temperature, cut tablespoon-sized pieces
  • ½ cup lemon curd at room temperature

Instructions

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  1. Combine egg whites, sugar and salt in a double boiler (or use a large, heat-proof mixing bowl set over a pot of gently simmering water–the bottom of the bowl should sit over, but not touch, the water below). Whisk vigorously until doubled in volume and sugar is completely dissolved (will read 160 degrees F on an instant-read thermometer).
  2. Return bowl to stand mixer fitted with the whisk attachment. Beat on medium-high speed until meringue is about tripled in volume and forms stiff, glossy white peaks. At this point it should also feel cool to the touch (measuring 80ºF or below) - this is the most important thing to check, as your buttercream will curdle if the meringue is still too warm.
  3. With the mixer running on medium speed, add 1 chunk of butter at a time, increasing speed and mixing until butter is completely incorporated before adding the next piece. Your buttercream will start to soften, going from stiff peaks to soft and almost soupy, but as you continue to add butter it will thicken up again. If at any point it begins to curdle, stop adding butter and increase mixer speed to high, beating until it comes together again before adding the remaining butter.
  4. If frosting is still soupy after adding all the butter (very likely if your kitchen is on the warm side) pop it in the fridge for 15 to 20 minutes to firm it up a bit, then return to the mixer and beat on medium-high for a few minutes until thick, smooth, and fluffy.
  5. On the other hand, if your frosting seems too thick and almost greasy, it's likely too cold. In which case, gently melt about 1/4 cup of the buttercream in the microwave (10-15 seconds on half power), then drizzle into mixer running on low. Increase speed to medium-high and beat for 2 to 3 minutes or until light and fluffy.
  6. Switch over to the paddle attachment and add lemon curd. Mix on low speed for a few more minutes until curd is fully incorporated (mixing on low speed will also help remove excess air bubbles).
  7. Buttercream can be made ahead of time, refrigerate with a layer of plastic wrap pressed to the surface. Before frosting, let come to cool room temperature then return to the stand mixer and re-whip on medium-high speed for 3 to 5 minutes or until light and fluffy once again.