16ouncesunsalted butter(454g) room temperature cut into 1-inch pieces
1teaspoonpure vanilla extractoptional (4.9mL)
¼teaspooncream of tartar(0.84g)
Beat the egg whites, salt, and cream of tartar, slowly add in ⅓ cup of sugar and continue beating until soft peaks form.
While the eggs are getting whipped add the remaining sugar and ⅓ cup of water into a medium pot and place on medium-low heat.
Stir until sugar melts and becomes clear.
Maintain at medium-high heat until temperature reads 235-240F.
Drizzle the sugar into the mixer immediately. At this point the meringue should be at the soft peak stage.
Run mixer until meringue is cool/tepid.
Switch to a paddle attachment. Add room temperature butter into running mixer one tablespoon piece at a time.
Add the salt and vanilla if using.
Beat until butter is combined and mixture has reached a silky consistency.
Eggs are easier to separate when cold, but egg whites whip up easier when closer to room temperature. I recommend separating them in advance if you have the time. In addition, allowing the egg whites to sit gives them a chance to relax, which improves their elasticity during the whipping process.
It is essential to have a clean and dry bowl for whipping the egg whites. The egg whites cannot contain any egg yolk whatsoever. If the bowl is not completely clean or yolk-free, it prevents your meringue from setting up.
If your equipment or bowl has grease on it, wipe down everything with lemon juice or vinegar.
Monitor the temperature of your sugar syrup closely, you don’t want it to get too hot.
Make sure you are using a medium pot as the sugar mixture will bubble as it heats up and will overflow out of a small pot.