Before you make this frosting, make sure that you use a fresh, soft bag of brown sugar to prevent any hard lumps of brown sugar in the buttercream.
Add 2 cups of unsalted butter, 1 cup of brown sugar, 1 Tbsp vanilla extract, and 1/2 tsp salt into a large bowl or the bowl of a stand mixer. Beat on a medium-high speed for 2 minutes with a stand mixer and paddle attachment or hand mixer. The mixture should get lighter in color as air is whipped into it.
Then let the mixture sit for about 5 minutes to give the brown sugar time to dissolve. After 5 minutes, rub a bit of the frosting between your fingertips. If it feels smooth, move on to step 4. If you still feel a lot of sugar granules, beat the mixture on a medium-high speed for another minute, then let it rest for another 5 minutes and test it again. Repeat until the frosting feels smooth.
Gradually mix in 7 cups of powdered sugar and 1/4 cup of heavy cream on a low speed.
Continue to mix on a low speed for a few minutes until the desired consistency is reached. If the frosting seems too thick, add additional cream (1 Tbsp at a time). If the frosting seems too thin, add in more powdered sugar (1/4 cup at a time).
Cover the frosting flush with plastic wrap to prevent it from crusting or place it in a piping bag with your favorite frosting tip. This frosting is amazing on cakes, cupcakes, and cookies!
This frosting can sit at room temperature for 2 days, be stored in the fridge for up to a month in an airtight container, or stored in the freezer for 3 months.
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Notes
If you need to make any substitutions or swaps in this recipe, please check out the section on ingredient substitutions above.
Yield
This recipe makes about 7 cups of frosting. If needed, this recipe can be halved or doubled. A double batch can be made in a 5 qt KitchenAid mixing bowl.I usually make one batch to frost three dozen cupcakes with large swirls or to fill and frost a 7- or 8-inch layer cake.
Tips for Making the Best Brown Sugar Buttercream Frosting
Make sure the butter is at room temperature before making your frosting.
If your powdered sugar contains cornstarch (most brands in the US do) there's no need to sift the powdered sugar.
Make sure your buttercream has the right consistency! This will make it much easier to use.
If you are making this frosting for a cake, mix the buttercream on the lowest speed at the end of the process for a couple minutes to get out any extra air that might have been incorporated during the mixing process.
Making This Brown Sugar Frosting in Advance and Storage Tips
This buttercream can sit out at room temperature for up to 2 days or be stored in an airtight container in the fridge for up to a month. This frosting can also be stored in the freezer for up to 3 months! Just be sure to give it a good stir once it thaws to make it nice and smooth again.A frosted cake can last in the fridge for a week, or in the freezer for a month. The buttercream locks in the moisture and keeps the cake fresh and delicious!