Mix buttercream frosting, 1/2 cup pasteurized protein from a carton, room temperature (120 g), 3 1/2 cups icing sugar (454 g or 1 pound a box), 1 1/2 cups or 3 sticks unsalted butter, room temperature (339 g), 1 tablespoon vanilla extract or vanilla bean paste (12 g), 1/2 teaspoon fine salt (3 g), tools and equipment, stand-up blender or electric hand blender. Butterscotch, not-so-sweet: Place 1/2 cup room-temperature pasteurized protein and 3 1/2 cups powdered sugar in a bowl in a stand-up blender (or a large bowl if you plan to make it with a hand blender).
Mix at low speed. Once all the powdered sugar has been added, stir in a blender on high for 5-10 minutes until the meringue has a firm peak. Replace the agitator attachment with a paddle attachment. Once the cream is fully made, this will help make it super smooth. Stir 1 1/2 cups or 3 bars of room temperature butter on low heat, one piece at a time. Wait until each stick of butter is well mixed before adding the next.
Once the butter is added, stir on medium speed for another 5 minutes until the frosting looks fluffy. If the frosting cracks or becomes sticky once you add butter, don't worry! Just keep stirring and it will return to its original shape after 5-10 minutes. When in doubt, keep mixing! Add 1 tablespoon vanilla extract and 1/2 teaspoon salt and stir on low speed until combined. Stir by hand with a rubber spatula for a few more minutes to make the frosting silky. Then use as needed! This frosting is great on multi-layered cakes, cupcakes, and macarons.
The spectrum made about 4 cups of frosting, enough to frost a 6-inch or 7-inch cake or 3 dozen cupcakes. Unless you have a commercial size stand up mixer, I don't recommend doubling this recipe. Egg whites and powdered sugar will not be stirred properly to keep the frosting properly consistent. Tips for making the best mixed cream cream. Stop sifting through your powdered sugar! Most U.S. brands contain cornstarch to prevent clumping, which means no screening is required. Filter only if you notice lumps in the powdered sugar. Make this frosting ahead of time, or save the rest of the frosting! It can be stored in an airtight container in the refrigerator for up to 2 weeks. After thawing, be sure to stir it well with a hand blender or stand up blender to keep it in good consistency again.
Frosted cupcakes can be left at room temperature for up to 2 days or in an airtight container in the refrigerator for up to 5 days. A frosting cake can last up to a week in the refrigerator or up to a month in the freezer. If you freeze the cake, transfer it to the refrigerator the night before you plan to eat it. This will help it thaw gradually and minimize any temperature shocks. About 30 minutes before you intend to cut the cake, take the cake out of the refrigerator.
If you have a stand up blender, use a stand up blender to make this recipe! You can use a hand blender, but it takes about twice as long to stir the meringue. Make sure the butter is at room temperature! If not, the frosting will crack or become viscous, which may take longer to reach the proper consistency. If the frosting cracks or becomes sticky once you add butter, don't worry! Just keep stirring and it will return to its original shape after 5-10 minutes. When in doubt, keep mixing! Once you've whipped the whites and powdered sugar, switch to the paddle attachment! This will help make the frosting aesthetically pleastically smooth. Seal the top of the piping bag with a rubber band to prevent any frosting from seeping out of the top of the bag, making the piping bag easier to use. If you make this frosting for a cake, mix the cream at the lowest speed for a few minutes at the end of the process to expel excess air that may have been mixed in during the mixing.