This is a nice, basic vanilla buttercream. It will stay soft
because there is no meringue powder in it. Meringue powder will cause a
frosting to "crust", which can be a good thing, if you want it.:
8 ounces (2 sticks) unsalted butter, at room temperature
2 pounds (7 1/2 -8 cups) confectioners' sugar
1 teaspoon vanilla extract
1/2 cup heavy cream
Tiny pinch of salt(to cut the sweetness)
Food coloring (optional)
In a stand mixer on medium speed, beat the butter until fluffy. On low
speed, add the sugar in batches, increasing the speed to high after
each addition is incorporated. Scrape down the bowl as needed. Add the
vanilla extract and cream in a steady stream on low speed until
incorporated. Add a few drops of food coloring, if desired.
Beat on high speed for 8-10 minutes, until light and fluffy.