Add the butter, powdered sugar, salt, vanilla extract, and 1 Tbsp almond milk to a large mixing bowl. With a handheld mixer, mix everything together until smooth. The frosting will be very thick at this point.
Now add the remaining 1 Tbsp of almond milk, along with the food coloring of your choice, if using. Mix again until the color has incorporated and that last Tbsp of almond milk has thinned the frosting out a bit.
Buttercream frosting is done. Use it to frost cookies, cakes, etc.
Notes
This recipe easily doubles or triples. Just don't multiply the salt or vanilla extract measurements; keep the salt at 1/8 tsp and the vanilla extract at 2 tsp.This frosting is gluten-free.This frosting can easily be made vegan by using your favorite vegan butter, such as Earth Balance Buttery Sticks.