- Preheat the oven to 350˚F. Bring a large pot of lightly salted water to boil. Add tortellini and cook until just tender.
- While pasta cooks, melt the butter in a pot set over medium heat. Stir in flour, mix until well combined and cook one minute. Slowly whisk in 1 cup of the warm milk into the flour mixture. When mixture becomes thick, slowly whisk in remaining milk. Bring this white sauce to a simmer, simmer two minutes, and then remove from the heat.
- Stir 1/4 cup chopped basil or parsley and Asiago and mozzarella cheeses into the sauce, and then season with salt and white pepper.
- When cooked, drain the tortellini well and place in 13- x 9-inch casserole. Spoon the sauce over the tortellini and sprinkle with Parmesan cheese. Bake tortellini, uncovered, 25-30 minutes, until golden brown and bubbling. Sprinkle with a little chopped basil or parsley and serve.
Note: The milk for this recipe could be warmed in the microwave. Warming it before using it to make the sauce will cause the latter to come to a simmer more quickly and, in turn, make it less likely to scorch on the bottom during the process.
Recipe Options: To make this casserole ahead and bake later, or to freeze and bake later, cool to room temperature after pouring on the sauce and sprinkle on the Parmesan cheese. Cover and store in the fridge, or in the freezer, until needed. Thaw the frozen casserole in the fridge overnight before baking. Baking time will be 5-10 minutes longer because you are starting from cold.
If you're only feeding one or two, divide the tortellini and sauce among small baking dishes. Cool unneeded portions to room temperature. Tightly wrap, label and freeze for another meal. Thaw them in the fridge overnight before baking. Baking time for smaller casseroles will be shortened by about 10 minutes.