Sarah's Italian Meringue Buttercream

Step 1
Pour egg whites into the clean bowl of a stand mixer fitted with a whisk attachment; beat at medium speed until frothy. Gradually add 1/4 cup sugar, continuing to beat until stiff peaks form.

Step 2
Combine remaining 1 cup sugar and water in a small saucepan. Attach a candy thermometer to the saucepan and place over low heat. Cook until syrup reaches 244 degrees F (117 degrees C) or until a small amount of syrup dropped into cold water forms a firm but pliable ball.

Step 3
Increase mixer speed to high and pour syrup in a slow and steady stream down the side of the bowl, beating until combined, 1 to 2 minutes. Reduce speed to medium-high and continue beating until meringue is stiff and the sides of the bowl feel barely warm, 3 to 4 minutes more.

Step 4
Beat in butter 1 tablespoon at a time until smooth. Switch to the paddle attachment, add vanilla extract, and beat on high until buttercream is light and fluffy, 4 to 7 minutes.