1. Cook tortellini according to directions listed on package. 2. Meanwhile, in a large deep skillet or saucepan, melt butter over medium heat. Add garlic and sauté 30 seconds. Then add flour and onion powder and cook, stirring constantly, 1 minute. 3. While whisking, slowly pour in milk and cream. Whisk until smooth. Cook, stirring constantly, until mixture begins to simmer. Then add tomatoes and spinach and salt and pepper to taste. Cook several minutes longer until sauce has thickened and spinach has wilted. Add parmesan cheese and stir until melted. Remove from heat. 4. toss prepared and drained tortellini into sauce mixture (note that as the pasta rests, the sauce will seem thicker and it will sort of soak into the noodles. So if you won't be serving it for ten minutes or so, you can stir in some pasta water, milk or cream to thin it out a little). 5. Serve warm with additional parmesan cheese sprinkled on top.