Step 1

Peel and devein shrimp; reserving shells. Cover shrimp with plastic wrap, and refrigerate until ready to use. Bring 4 1/2 cups water and reserved shells to a simmer in a large saucepan over medium-high. Remove from heat; let stand 15 minutes. Strain stock, and discard shells. Set aside 4 cups shrimp stock.

Step 2

Melt butter in a large heavy saucepan over medium. Whisk in flour; cook, whisking constantly, until light blond, about 3 minutes. Add onion, celery, bell pepper, and garlic; cook, stirring occasionally, until vegetables are tender, about 8 minutes. Add Creole seasoning, bay leaf, and thyme; cook, stirring constantly, 1 minute. Add stock; cook, stirring occasionally, until slightly thickened, about 30 minutes.

Step 3

Add shrimp and crabmeat; cook over medium, stirring occasionally, until shrimp is fully cooked, 3 to 5 minutes. Remove and discard bay leaf and thyme sprigs. Season with kosher salt to taste; serve over rice