White Chocolate Swiss Meringue Buttercream Frosting

• Before making this frosting, be sure to thoroughly clean your mixing bowl. If there’s any grease, it can make it difficult to whip up the meringue. In a medium-sized pot, add about 1 inch of water and bring to a simmer.
• Add 8 egg whites and 2 1/2 cups of granulated sugar into a large, heat-proof bowl.
• Place the bowl on top of the pot filled with simmering water. The bowl should create a seal over the pot. Make sure the water isn’t actually touching the bottom of the bowl, or it can cook the egg whites.
• Whisk the mixture constantly for about 3 minutes, until it reaches 160°F / 71°C. You can test the mixture to see if it’s ready by rubbing a tiny bit between your fingertips. The sugar should be fully dissolved, and it should feel super smooth and hot to the touch.
• Once it reaches this stage, lift the bowl away from the pot and dry the bottom with a towel. Pour the mixture into the bowl of a stand mixer and beat on a medium-high speed with a whisk attachment. Mix for about 10 minutes, or until you have stiff, glossy peaks that stick straight up. While the meringue whips, I like to add something cold around the base of my bowl. I find the meringue stays quite warm while it whips up, and placing a bag of frozen veggies around the base of the bowl helps cool it back to room temperature. This can prevent your buttercream from becoming soupy in the next step.
• Next, melt 1 cup of white chocolate chips in the microwave or with a double boiler. If you use a microwave to melt the white chocolate, heat it in 15-second intervals, stirring between each interval. Stir until smooth, then set aside to cool. The white chocolate needs about 10 minutes to cool down so that it doesn't melt the butter in the frosting.
• At this point, I recommend feeling the bottom of the mixing bowl with your hand. If it feels pretty much room temperature, then add in the butter. If it still feels warm, either wait another 15 minutes to add the butter or pop the bowl into the fridge for 5 minutes to help it cool down. This will help prevent soupy buttercream.
• Then mix in 2 cups of unsalted butter at a medium speed, 1 stick at a time. Scrape the sides and bottom of the bowl with a rubber spatula as needed. The frosting should have a thick, whipped consistency once all the butter is mixed in. If it looks lumpy or broken, keep mixing until it looks fluffy and thick. If it doesn't seem to come together after an additional 10 minutes of mixing, check out the troubleshooting section in the post above.
• Once the consistency is right, swap out the whisk attachment for a paddle attachment and add in the melted and cooled white chocolate (it should still be fluid, but lukewarm to the touch), 2 tsp vanilla extract, and 1/2 tsp fine salt. Continue mixing on a low speed for a couple of minutes to make the frosting extra smooth.
• Then comes the fun part! This buttercream can be used to frost everything from cakes to cookies. It pipes like a dream and is also great for filling layer cakes. It can sit out at room temperature for up to 2 days or be stored in the fridge for up to 2 weeks.