Melt butter in a saucepan and add onion and garlic; saute until onion is transparent. Stir in the flour to make a roux and cook 5minutes, stirring often. Mix the hot water, chicken stock and half and half. Add mixture slowly to roux, stirring constantly. Allow to cook 5 minutes.(Sauce should have the consistency of honey). Add salt, sugar, hot sauce, lemon juice, cayenne, and parmesan cheese to sauce. Stir to blend. Do not allow to boil. Add Velveeta to sauce and stir until melted. Add salsa and sour cream to sauce and blend. Makes 5 cups.