In a large sauce pot, melt butter. Add mushrooms, thyme and garlic; sauté until fully cooked, approximately 5-7 minutes. Remove from heat. Puree half of mushroom mixture and return to pot.
In the same pot, combine milk, water and Mushroom Base using a wire whip. Heat until boiling, stirring frequently.
In a bowl using a wire whip, blend half and half and Dry Roux into a smooth slurry. Set aside.
Gradually pour the slurry into the boiling soup mixture, stirring constantly. Reheat to a boil, stirring frequently. Reduce heat and gently boil for 1 minute, stirring occassionally.