In a medium frying pan,melt the butter over low heat. Add the garlic and cook, stirring occasionally and mashing the garlic with the back of a wooden spoon,until it is soft and golden, 10 to 12 minutes. Stir in the sage,salt and pepper.
In a large pot of boiling salted water, cook tortellini until just done,about 4 minutes for fresh and 12 for frozen. Drain the pasta and return to pot.
Add the butter and parsley and toss over low heat until the pasta is thoroughly coated with the butter, about 1 minute.