1. Heat broiler, with rack in top position. In a medium saucepan, cook bacon until browned and crisp. Transfer to paper towel. Add onion and garlic to pan and season with salt and pepper. Cook, stirring occasionally until onion softens. Add flour and cook, stirring, for 30 seconds.

2. Slowly add milk, whisking constantly. Add tortellini and bring to a boil over medium-high, stirring occasionally. Reduce to a simmer; cook, stirring often, until liquid has thickened, about 4 minutes. Remove from heat; stir in bacon and ¼ cup parmesan. Transfer to a 2-quart baking dish and top with more parmesan. Broil until top is golden brown, 3-5 minutes.