In a mixer with paddle attachment, whip butter till light and fluffy.

On low, slowly add powdered sugar.

Add milk, salt, and vanilla.

In a microwave melt chocolate in 2 30 seconds blasts. It might not look melted, but try stirring before cooking longer.

After the chocolate has cooled to lukewarm, but is still runny, drizzle into frosting and mix well.

If frosting looks rough after chocolate, add an extra ½ tbsp milk and mix again.