Melt 4 tablespoons of butter in a large pot over medium heat. Add 1 diced onion and 2 minced garlic cloves, sautéing until the onion is translucent, about 5 minutes.

Gently fold in 1 pound of crab meat and 1 pound of peeled shrimp. Cook for 3–4 minutes, stirring occasionally, until the shrimp turn opaque and the crab is heated through.

Sprinkle in 1/4 cup of flour, stirring consistently for about 2–3 minutes to create a roux.

Gradually whisk in 4 cups of seafood stock, bringing it to a gentle simmer for about 5 minutes.

Once simmering, add 1 teaspoon of dried thyme, 1 tablespoon of Old Bay seasoning, and salt and pepper to taste.

Reduce the heat to low and gently stir in 1 cup of heavy cream, allowing it to blend for at least 10 minutes.

Taste and adjust the seasoning as needed before ladling into bowls.