Combine the egg whites, sugar, salt, and vanilla bean together in an clean bowl. Set the bowl over a pan of water and turn the heat on medium low. You donít need the water to even simmer, you just want it hot enough to steam, since steam is what actually heats the whites.
Whisk frequently to prevent an egg white omelet forming on the sides, but continual mixing isnít necessary. Aim to get the mixture to at least a 145į for food safety reasons, but reaching 150į would make for a nice margin of error. If your egg whites are at room temperature, this wonít take very long, maybe just a few minutes. Whites straight from the fridge will take longer.
When the mixture is sufficiently hot, remove from the heat and use the whisk attachment to whip on medium high speed until the mixture has doubled in volume and turned snowy white. Continue whipping until the meringue is cool. Use your hands to feel the bowl itself, rather than simply testing the temperature of the meringue. You want it to feel perfectly cool to the touch with no trace of warmth.
Note: if you are using a glass or ceramic bowl, even if the meringue has cooled, the bowl itself may still be quite warm and continue conducting heat into the buttercream over time. If you are using a glass or ceramic bowl, transfer the meringue to a new bowl before proceeding or continue mixing until the bowl itself is cool.
Turn the mixer down to medium-low and begin adding in the butter, one chunk at a time. If you didnít let your meringue cool enough, this is when youíll really regret it. By the time youíve added all the butter, you may need to scrape down the bowl to fully incorporate any butter or meringue thatís stuck at the sides.
Finally, splash in some vanilla extract or what have you. Just keep adding a 1/4 teaspoon at a time until it suits your tastes.
The buttercream freezes beautifully. I always have a few containers in my fridge to pull out when I want to make macarons or layer cake.
Caramel: after making the buttercream, whip in 16 ounces of room temperature caramel, or more to taste.
Cranberry: after making the buttercream, drizzle in up to 8 ounces of room temperature Cranberry Syrup. Unlike the caramel variation, you canít keep adding Cranberry Syrup to taste, as too much will cause the buttercream to break.
Cream Cheese: reduce the butter to 16 ounces, and replace the rest with 16 ounces cream cheese, softened to room temperature. After finishing the buttercream, whip in 1 ounce lemon juice to reinforce the cream cheese tang.
Green Tea: after finishing the buttercream, whip in 2 Tablespoons matcha powder, or more to taste. Matcha has a naturally bitter flavor, so start small and add the rest a little at a time until itís just to your liking.
For a phenomenal online tea source visit Essencha. I use their matcha sawa in all my ďgreen teaĒ recipes. In the Lexington area, you can find matcha at the Dong Yang Market off Clayís Mill.
Milk Chocolate: milk chocolate doesnít pack enough punch to stand up to all the sugar and butter in this recipe, so youíll need a little dark chocolate for the flavor to shine through.
While whipping the meringue, melt 8 ounces milk chocolate and 5 ounces dark chocolate in the microwave, stirring with a spatula every 30 seconds to prevent scorching. Once the meringue has cooled and youíve added all the butter, turn the speed down to low and add the melted chocolate all at once. Move quickly, as the melted chocolate can form chips against the side of the bowl. Increase the speed to to medium-high and whip until homogenous.
Spiced Chocolate: especially nice with Chai Cocoa Cupcakes. Follow the Milk Chocolate variation, using all dark chocolate instead. After finishing the buttercream, whip in 1 teaspoon ground cinnamon, or more to taste.
Peanut Butter: omit the salt in the recipe. After whipping in the butter, add as much peanut butter as you like (commercial varieties work better). This may sound obscene, but Iíve added up to 32 ounces of peanut butter. Yes, it was insanely delicious.