Step 1

Add the butter to a sauce pan on medium heat.  Whisk in the heavy cream and heat for a minute.  Then add in the mascarpone cheese, salt and pepper.

Step 2

Once the mascarpone is melted, add in the cheddar cheese and stir.  Cook over medium low heat for a few minutes, or until the sauce has thickened to your liking.  Mine took a little over 3 minutes.

Step 3

Once thickened, add in the lemon zest and serve.