In a medium-sized pot, add about 1 inch of water and bring to a simmer.
Before making the frosting, be sure to thoroughly clean your mixing bowl by wiping it down with a bit of vinegar or lemon juice. If there’s any grease, it can make it difficult to make the meringue.
Add 4 egg whites and 1 cup of sugar-free sweetener like Swerve or Allulose into a heat-proof mixing bowl.
Place the bowl on top of the pot filled with simmering water. Make sure the water doesn't touch the bottom of the bowl. The bowl should create a seal over the pot.
Whisk the mixture constantly for 3-5 minutes, until it reaches 160°F/71°C. At this point, the mixture should feel smooth and hot to the touch with your finger.
Lift your bowl away from the pot and dry the bottom with a towel. Pour the mixture into the bowl of a stand mixer. Beat on medium-high using a whisk attachment. Mix for 5-8 minutes, or until you have stiff and glossy peaks. You can also use a hand mixer, but it will take a bit longer.
At this point in time, the mixing bowl should be room temperature. If it’s warm, it will melt your butter!!
Mix on a medium speed and add in 3/4 cup of room temperature unsalted butter in small chunks.
Then add in 1/2 tsp salt, 2 tsp vanilla bean paste or extract, and 1 tsp almond extract. If you want to color this frosting, add in gel food coloring at this point and mix on a low speed until fully incorporated.
When all butter is mixed in, scrape the sides and bottom of the bowl with a rubber spatula and continue mixing on a low speed for about 3 minutes.
The frosting should have a thick whipped consistency at this point. If it looks lumpy or broken, keep mixing until it looks smooth and thick.
Place the frosting into a large piping bag fitted with your favorite frosting tip and pipe on each cooled cupcake. I used a Wilton 1M to decorate these cupcakes.