Preheat the oven to 400°F (200°C).

Cook 20 oz tortellini according to the package instructions; drain and set aside.

While the tortellini cooks, dice or cut 8 oz cream cheese into pieces and place them in a large ovenproof skillet with 1 1/2 cups chicken or vegetable stock. Heat over medium-low, stirring or whisking until the cream cheese melts and the mixture becomes a smooth sauce, about 5–10 minutes.

Add 6 cups loosely packed baby spinach leaves to the sauce (in batches if needed) and cook, stirring, until the spinach wilts, about 3–5 minutes.

Add the cooked tortellini to the skillet and gently stir to coat the pasta evenly with the sauce.

Sprinkle 1 cup shredded Colby Jack or mozzarella cheese evenly over the top.

Place the skillet in the preheated oven and bake 7–10 minutes, until the cheese is melted and the edges are bubbling.

Remove from the oven and let rest 2–3 minutes before serving.