Melt butter in a heavy pot over medium heat. Sauté shallot, celery, red peppers and mushrooms until tender. Stir in garlic. Add flour and black & white peppers.
Cook 4–5 minutes, stirring often to incorporate flour. Whisk milk and half & half into flour mixture until smooth. Add thyme and clams.
Simmer until slightly thickened being careful not to boil. Taste and add salt as needed. Garnish with crumbled bacon and sprigs of thyme.