In a large bowl, whisk together the powdered sugar, butter, 1 tablespoon milk, and vanilla.
Slowly whisk in the remaining 1 tablespoon milk or until a pourable consistency.
If the glaze is too thin, add more sugar.
To test for consistency, take a spoonful of glaze and drizzle it back into the bowl. It should leave a ribbon trail for a few seconds before blending back into the glaze.
Pour over cooled cake as desired.
Let harden at room temperature for 2 hours or in the fridge for 30 minutes.
