For Cream Sauce: In a heavy saucepan over medium low heat, melt the butter and stir in the flour. Cook until it is golden and frothing. Add the milk and chicken stock, stir until smooth and thickened. Cook for about a minute and add the remaining ingredients. Heat through and remove from heat.
Next, saute the mushrooms in 2 tablespoons butter until just heated through; add the parsley and toss. In a buttered baking dish, combine the spaghetti with half the cream sauce, the mushrooms and parsley.
Add turkey to the remaining cream sauce and mix well. Add to above, toss. Top with Parmesan cheese. Bake at 350° F. for 30 minutes then broil the top to brown.