Sauté the chopped onion in a skillet with 1 tablespoon of butter until translucent and fragrant. Add the shrimp and cook until pink and opaque. Fold in the lump crab meat and remove from heat.

Melt 4 tablespoons of butter in a saucepan over medium heat. Whisk in the flour, then gradually pour in the broth while stirring until the sauce thickens.

Add sour cream and cream cheese to the sauce, stirring until smooth. Season with salt and pepper.

Warm tortillas in a skillet until pliable. Fill each with the seafood mixture, roll tightly, and place seam-side down in a greased baking dish.

Preheat oven to 350°F (175°C). Pour the creamy sauce over enchiladas and top with shredded cheese.

Bake for 25-30 minutes until the cheese is melted and bubbly. Let cool for a few minutes before serving.

Serve warm, garnished with cilantro and sides like cilantro lime rice or salad.