In a stand mixer fitted with the paddle attachment, beat the butter until light and fluffy, about 2–3 minutes.

Add the cold mascarpone cheese and beat just until combined and smooth do not overbeat.

Sift in the cocoa powder and powdered sugar. Add salt and vanilla.

Mix on low to combine, then increase speed and beat until smooth and creamy.

If the frosting is too thick, add cream or milk one tablespoon at a time to reach desired consistency.

Use immediately or store in the fridge for up to 3 days. Rewhip before using.