Start by washing some button mushrooms, then slice them up and saute in a skillet with 1 minced garlic clove in a bit of olive oil. Add some snipped parsley, and cook for 5 to 8 minutes. Cook the tagliatelle to al dente, and drain. Once the mushrooms are cooked, add 3/4 cups half-and-half, and heat through for 2 to 3 minutes. Serve the tagliatelle coated in the mushroom sauce and garnished with chopped parsley.