Preheat the oven: Set your oven to 375°F (190°C). Lightly grease or line a casserole dish with parchment paper to prevent sticking and make cleanup easy.
Prepare the garlic base: In a large skillet, heat olive oil over medium heat. Add the chopped garlic and sauté for 1–2 minutes until fragrant and lightly golden. Avoid browning the garlic too much to prevent bitterness.
Make the cheese sauce: Pour in the milk and stir in the Italian seasoning. Heat the mixture gently until warm but not boiling. Reduce the heat to low, then add the cubed Velveeta and shredded cheese a handful at a time. Stir constantly until everything melts into a smooth, creamy sauce.
Combine pasta and fillings: Turn off the heat and gently fold the cooked tortellini and quartered pepperoni into the cheese sauce. Stir until the pasta is evenly coated and the pepperoni is well distributed throughout the mixture.
Assemble the casserole: Transfer the cheesy tortellini mixture into the prepared casserole dish. Spoon small dollops of pizza sauce across the top and lightly swirl it into the mixture with a spoon or spatula for a marbled look.
Add the toppings: Arrange the sliced pepperoni evenly on top of the casserole. Sprinkle with the shredded mozzarella to create a golden, bubbly crust when baked.
Bake to perfection: Place the dish in the preheated oven and bake for 25 minutes, or until the top is golden brown, bubbling, and irresistibly cheesy. The casserole should be heated through with the cheese fully melted.
Cool and serve: Remove the casserole from the oven and let it rest for 5 minutes before serving. This helps the sauce thicken slightly and makes it easier to portion. Serve warm, garnished with extra Italian herbs or crushed red pepper for a touch of spice.
