Take the cream cheese out of the fridge at least 30 minutes prior to starting the recipe, or microwave it for 20-30 seconds. It needs to be very soft. Preheat your oven to 375F and move the rack to the top third of the oven.
Boil water for the tortellini, and cook it one minute less than package directions indicate. Drain and add it to a 9x13 casserole dish.
Meanwhile, add the butter to a skillet over medium heat. Once it's melted, add the garlic and cook for 30 seconds.
Add in the cream cheese and heavy cream. Stir/whisk constantly until the cheese has melted in and it's thickened up a bit (this shouldn't take more than 4-5 minutes). Don't let the sauce get too thick because it'll continue to thicken up/reduce in the oven. If it becomes a bit too thick, add in a splash more cream.
Stir half the parmesan cheese into the sauce and then take the skillet off the heat. I add a bit of salt & pepper to the sauce.
Pour the sauce over the tortellini and then toss it and spread it out in an even layer.
Top the tortellini with the rest of the parmesan and the mozzarella.
Bake, uncovered, for 12-15 minutes until the cheese has melted, and then broil it for a few minutes to brown the cheese a bit (watch it carefully).