In a large skillet, melt a tablespoon of butter over medium heat. Add 0.5 cup diced onions, sautéing for 3-4 minutes until they become translucent.

Next, add 1 lb chopped shrimp and cook for 3-5 minutes until the shrimp turns pink and opaque. Lastly, gently fold in 8 oz lump crab meat, allowing it to warm through for an additional 2 minutes before removing from heat.

In a medium saucepan, melt 3 tbsp butter over low heat. Stir in 3 tbsp all-purpose flour to create a roux, cooking it for 1-2 minutes until light golden.

Gradually whisk in 1.5 cups broth, and bring the mixture to a simmer. Allow it to thicken for about 3-5 minutes until you achieve a creamy consistency.

Once the sauce has thickened, reduce the heat to low and stir in 0.5 cup sour cream and 4 oz cream cheese. Continue mixing until smooth and creamy, approximately 2-3 minutes.

Preheat your oven to 350°F (175°C). Take 8 medium flour tortillas and lightly warm them. Spoon an even amount of the seafood filling onto each tortilla, roll them up, and place seam side down into a greased baking dish.

Once all the enchiladas are in the dish, pour the creamy seafood sauce evenly over the top. Sprinkle 2 cups shredded Monterey Jack cheese over the sauce.

Place the baking dish in the preheated oven and bake for 25-30 minutes, or until the sauce is bubbly and the cheese has melted to a beautiful golden color.