Once you learn the technique of making these two butter creams, you'll never go back to frosting out of a can. There are two basic techniques and they both involve cooking the egg whites. My method is to combine both the Swiss technique with the Italian technique.
Swiss/Italian Meringue Butter cream Frosting
4 large egg whites (about 4 oz)
1 cup granulated sugar divided (1/4 cup and 3/4 cup)
1/4 cup water
1 lb or 4 sticks of unsalted butter (room temperature)
1. Cut the butter into tablespoon-size pieces you can leave them on the wax paper or set aside in a medium bowl.
2. Put 3/4 cup of sugar into a heavy-bottomed 1-quart saucepan with 1/4 cup water. Gently stir to combine; I use the candy thermometer for this. Leave the candy thermometer in the saucepan, numbers facing down to balance the thermometer.
Place the saucepan with the sugar and water over medium-high heat. Partially cover with a lid to capture the evaporating water -- this helps to moisten the sides of the saucepan to prevent sugar crystals separating from the syrup.
3. Put the 1/4 cup sugar and egg whites in a mixer bowl, fit the bowl over a pan of simmering water and whisk constantly keeping the mixture over the the heat until it feels very warm and you don't feel any graininess from the sugar. (About 2-3 minutes.)
4. Put mixing bowl in a standing mixer fitted with the wire whip attachment set to medium then increase to high speed. When the whites are at stiff peak you have a meringue.
4. At the same time, the egg whites are whipping. Raise the heat to bring the syrup to 245F. When the syrup is at 245 degrees, remove the thermometer and slowly pour the syrup into the meringue while is it whipping. Aim for the space between the mixer bowl and the revolving wire whip or if you are like me, just pour it down the side of the mixing bowl. If you aim at the revolving whisk, you'll have to clean your bowl and start all over from the beginning.
5. After 1 to 2 minutes reduce the speed to medium for about 3 to 4 minutes or until the meringue is cooled.
6. Add the butter one tablespoon at a time. Increase the speed to high for one to two minutes to fully combine the butter with the meringue.
The following flavorings can be added to the base recipe for Swiss/Italian meringue butter cream for cupcakes or a layered cake.
1 teaspoon vanilla extract
1/2 cup bittersweet chocolate, melted
2 to 4 tablespoons (to taste) dark rum
2 to 4 tablespoons (to taste) amaretto
1/4 to 1/2 cup fruit puree (raspberry, strawberry, mango, etc.)
2 tablespoons lemon liqueur (lemoncello)
1 teaspoon orange oil or lemon oil