In a large bowl, beat butter and sugar at low speed until combined. Increase the speed to medium and beat until well combined, about 3 minutes. Scrape the sides of the bowl. Add vanilla and salt and beat until combined.
Reduce the speed to low and slowly add the almond milk until the frosting is soft and spreadable. Scrape the sides of the bowl as needed. Add melted chocolate and beat until well incorporated. Use immediately.