I like BraveTart's swiss meringue buttercream recipe.
Swiss Meringue Buttercream
10 oz egg whites
10 oz granulated sugar
2 lbs unsalted butter, cool room temperature.
Heat a small pot of water on medium heat. Place a small metal bowl over the pot. Add egg whites and sugar. Stir constantly to prevent egg whites from cooking. Heat to 150 degrees F for food safety. Next transfer egg/sugar mixture to a larger steel bowl and mix on high until stiff peaks form and bowl is cool to touch on the outside, about 10 minutes. Cut butter into 1 tbsp pieces. Add one at a time to the meringue and continue mixing on high. After all butter is added, mix for an additional 3 minutes to make buttercream fluffier. Now you are ready to frost!
Buttercream can be stored in a sealed container at room temperature for 2 days, in the refrigerator for up to 2 weeks or in the freezer for 2 months. Let come to a cool room temperature prior to using.