Bring a large pot of salted water to a boil. Heat 1 T. butter in a large skillet over medium. Add broccoli and garlic; season with salt and pepper. Cook, tossing occasionally, until broccoli is crisp-tender, 6 to 8 minutes (if skillet gets too dry, add a little water).

Cook tortellini in boiling water until al dente. Drain, reserving ½ c. pasta water; return tortellini to pot. Add broccoli mixture, tomatoes, and remaining 2 T. butter; season with salt and pepper, and toss enough reserved pasta water to create a sauce that lightly coats tortellini. Serve immediately.