Using a hand held mixer or standing mixer, cream the butter using a paddle or whisk attachment on medium high until pale yellow, about 4-5 minutes. If necessary, half way through scrape down the sides of the bowl and continue mixing.
Turn off the mixer and add powdered sugar and vanilla. Mix on low for a minute until it incorporates and starts to look crumbly.
Once crumbly, turn up the speed and continue mixing on medium to medium high, about 3-4 minutes until light and fluffy.
gauge the consistency. If the frosting is too thick, you can mix in a few tablespoons of milk or cream, 1/2 tbsp at a time, until it reaches the desired consistency.
Mix in black food coloring. The amount needed will vary depending on your type and brand, but you want it to be at least a medium to dark gray. At this point, you can either leave it to deepen overnight, or heat it up using the heating method.
To heat, either use an immersion blender to blend and smooth out, or transfer the frosting to a microwave safe bowl and heat in the microwave for 10-15 seconds.
Then, let firm up in the refrigerator for 15-20 minutes and stir by hand to remix.