Preheat oven to 350 degrees F. In a heavy-bottomed sauté pan, melt butter over medium-high heat. Add celery, onion, bell peppers and garlic. Sauté until vegetables are wilted, approximately 3-5 minutes. While vegetables are sautéing, whip egg yolks and evaporated milk until well blended and set aside. Sprinkle flour over seasoning mixture and blend well into the sauté pan to create a white roux. Do Not Brown. Using a wire whisk, add milk/egg mixture while stirring constantly to blend into roux mixture. Season to taste using salt, peppers, basil and thyme. Continue to blend, cooking 3-5 additional minutes. Remove from heat and fold 1/4 pound Cheddar cheese into the white sauce mixture and blend until cheese is totally melted. Place cleaned crabmeat into a Pyrex baking dish. Top with the cheese sauce, then sprinkle with remaining grated cheddar. Cover and bake until bubbly. Uncover then slightly brown the top of the casserole.