Cook tortellini as directed on package. Meanwhile, thaw the frozen shrimp in a colander using cold running water. Remove the tails. If using uncooked shrimp, devein and remove tails and then sauté in a teaspoon of the butter. Remove shrimp and set aside. Do not overcook. In a saucepan combine butter, heavy cream, and cream cheese. Simmer this until all is melted, and mixed well. Add the Leeks, Parmesan Cheese and garlic powder. Simmer this for 15 – 20 minutes over low heat. Toss the tortellini with the shrimp and sauce, coating well. Add the parsley or chives and serve.