Melt 4 tablespoons of butter in a heavy-bottomed pot over medium heat. Add 1 cup of finely chopped celery and 1 cup of sliced green onions. Sauté for 3-4 minutes until softened.

Sprinkle in ¼ cup of flour and stir for 1 minute to eliminate raw taste. This creates a roux to thicken the bisque.

Warm 2 cups of whole milk in the microwave for about 45 seconds. Gradually whisk the warm milk into the roux, stirring continuously for a smooth consistency.

Mix in 1 cup of heavy whipping cream, 2 tablespoons of tomato paste, and 1 tablespoon of Old Bay seasoning. Season with salt and pepper to taste.

Bring to a low simmer over medium heat, stirring frequently. Let it bubble for 5-7 minutes until it thickens.

Add 2 cups of cooked shrimp and 1 cup of crab meat, stirring gently to combine. Heat for 2-3 minutes until shrimp are pink and opaque.

Ladle the bisque into serving bowls. Garnish with freshly chopped parsley or chives before serving.