Mom's Favorite with Crawfish and Crab Sauce

6 (4 ounce) fillets of your favorite fish
kosher salt and ground black pepper to taste
1/2 cup butter
3 tablespoons light olive oil
2 shallots, minced
1/2 teaspoon minced garlic
3 tablespoons chopped fresh parsley
3 tablespoons all-purpose flour
1 cup half-and-half
white pepper to taste
1 (16 ounce) package frozen cooked crawfish tails, thawed
1 (6 ounce) can lump crabmeat

Preheat an oven to 350 degrees F (175 degrees C). Season the bass with salt and pepper; arrange in a baking dish and set aside. Melt the butter with the olive oil in a skillet over medium-low heat. Cook the shallots, garlic, and parsley in the melted butter and olive oil until softened, about 5 minutes. Add the flour and stir continually until completely incorporated into the mixture and the liquid is smooth. Pour the half-and-half into the mixture while stirring; cook and stir until thickened. Season with the white pepper. Gently fold the crawfish tails and crabmeat into the mixture, taking care to not break the crabmeat too much; cook another 1 minute. Spoon the mixture over the bass fillets. Bake in the preheated oven until the fish flakes easily with a fork, 15 to 20 minutes. Serve immediately.