Step 1

Beat the egg whites, salt and cream of tartar, slowly add in 1/3 cup of sugar and continue beating until soft peaks form.

Step 2

While the eggs are getting whipped add the remaining sugar and 1/3 cup water into a medium pot and place on medium-low heat.

Step 3

Stir until sugar melts and becomes clear.

Step 4

Maintain at medium-high heat until temperature reads 235-240F.

Step 5

Drizzle the sugar into the mixer immediately. At this point the meringue should be at the soft peak stage.

Step 6

Run mixer until meringue is cool/tepid.

Step 7

Switch to a paddle attachment. Add room temperature butter into running mixer one tablespoon piece at a time.

Step 8

Add the salt and vanilla if using.

Step 9

Beat until butter is combined and mixture has reached a silky consistency.