Preheat the oven to 325. In a glass baking dish, whisk together flour and melted butter until combined. Bake for 25-30 minutes, or until golden and crumbly. Set aside.
In a large pot, melt 1-2 tablespoons of butter and add celery, onion, and leeks. Cook on medium heat for about 3-5 minutes or until soft and slightly transparent.
Add all the remaining ingredients EXCEPT the butter/flour mixture, half & half, and clams. Bring to a boil, then reduce heat and simmer for about 10 minutes or until potatoes are cooked through and fork tender.
Add the butter/flour mixture into chowder and stir until thick. The mixture will be extremely thick.
Remove chowder from heat and stir in half & half until blended and smooth. Heat to serving temperature (do not bring to a boil), stirring occasionally. Once the chowder has thickened slightly, stir in the clams. Serve immediately.
How to Steam Fresh Clams ¼ cup water ½ cup chicken broth 6 cloves garlic, crushed 2-3 pounds fresh clams, cleaned