I know this post was made forever ago, but the below recipe has been a lifesaver

Swiss Meringue Icing

1/2 cup white sugar (cane or birch sugar would work really well)
2 large egg whites
3/4 cup (1 1/2 sticks) unsalted butter, room temperature - again, lard or vegetable fat would work
2 teaspoons vanilla extract
1/4 teaspoon ground cinnamon

For buttercream: put the sugar and egg whites in a large heatproof bowl over a saucepan of simmering water and whisk constantly, keeping mixture over the heat, until it feels hot to the touch, about 3 minutes. The sugar should be dissolved, and the mixture will look like melty marshmallow cream.

Pour the mixture into the bowl of a stand mixer fitted with a whisk attachment and beat on medium speed until it cools and forms a thick and shiny meringue, about 5 minutes. Switch to the paddle attachment and add the butter, one tablespoon at a time, beating until smooth. Once all the butter is in, beat the buttercream on medium-high speed until is is thick and very smooth, 6-10 minutes. Add the vanilla and cinnamon and whip for another 30 seconds until incorporated. Spread or pipe on cooled cake/cupcakes.