Boil broth with garlic, thyme and lemon pepper in a large heavy skillet until reduced to about 1 cup, about 6 minutes or so.
Meanwhile, cook tortellini in a pasta pot of boiling salted water (1 1/2 tablespoons salt for 4 quarts water) according to package directions. Drain.
Stir cornstarch into cream, then whisk into broth. Bring to a simmer, whisking, then continue to simmer 1 minute. Add asparagus and simmer until crisp-tender, about 2 minutes. Stir in cheese and tortellini and cook, gently stirring, until heated through.