Pre-heat oven to 325°F.
In a baking dish, stir together 3/4 cup melted butter and flour until smooth.
Cover and place in pre-heated oven and bake for 30 minutes.
Remove from oven and set aside.
Meanwhile, add remaining 1/4 butter to a large Dutch oven over medium heat.
Add the celery, onion, green peppers and leeks and sauté until tender; about 5 minutes.
Add the potatoes and clams to the pot, along with enough broth to cover everything; stir in salt, pepper, thyme and bay leaves.
Bring to a boil; reduce heat and simmer until potatoes are just tender; about 15 minutes.
Gradually stir in the baked flour and butter mixture until chowder is very thick.
Remove and discard bay leaves, then remove soup from heat and gradually stir in milk to reach desired consistency.
Stir in hot sauce; add additional salt and pepper, before serving, if needed.
