Fish with firm, thick fillets like grouper can be grilled, roasted, broiled or poached. The best method depends on the time and equipment you have available and the occasion you're preparing the fish for. Whichever technique you choose, grouper requires approximately eight to 10 minutes of cooking time for every inch of thickness, writes "How to Cook Everything" author Mark Bittman. The inside of the thickest part of the fish will appear opaque when it's fully cooked. Use a cooking thermometer to confirm that the fish has reached 145 degrees Fahrenheit before serving.
Hit the Grill
Grilling may be your best cooking option for grouper when the weather is warm and eating outside is part of the day's plan. Choose from grouper fillets -- with or without the skin -- steaks or the whole fish, scaled and well-cleaned. Marinate the grouper for approximately 15 to 30 minutes or simply drizzle it with olive oil and season with salt and pepper. Heat the grill to medium-high, scrape and lightly oil the grate and add the fish. Fillets and steaks 1 inch thick will require about 4 to 5 minutes per side, while a 2-pound whole grouper may need a few more minutes of cooking time on each side.
Use Your Oven
Baking grouper fillets in the oven takes little hands-on effort. It's the best method to use when you need to focus your attention on preparing side dishes to serve with the fish. Put a few tablespoons of vegetable oil, butter or a combination of both into a baking dish and place it in an oven heated to 450 degrees Fahrenheit. For more flavor, add lemon or lime juice and seasonings like minced garlic or ginger, spices and fresh or dried herbs. Once the oil is hot or the butter melted, place the grouper into the pan. Turn each fillet to coat both sides, sprinkle with additional seasonings, if desired, and bake for approximately 7 to 8 minutes.
Heat the Broiler
To prepare crispy, browned grouper fillets without a grill, broiling is your best option. Position the oven rack so the surface of the grouper will be about 4 inches from the heat source. While the broiler is heating, lightly coat a broiler pan with nonstick cooking spray or vegetable oil. A rimmed baking sheet can be used instead. Arrange the fillets on the pan, brush them with oil or melted butter and season with your choice of salt, pepper, herbs and spices. Broil the fish, rotating the pan every 2 minutes and basting the fillets with the juices that collect at the bottom or with additional butter or oil.
Experiment With Poaching
According to Bittman, poaching thick white fillets like those from grouper yields tender fish in a flavor-rich sauce, making it one of the best ways to serve grouper in a formal dinner setting. Tomato sauce, wine, stock or broth, water or a combination of any of these can be used as the poaching liquid. In a large, deep skillet, sauté chopped onions until they're soft, then add the liquid, using approximately 4 cups for every three grouper fillets. Boil the liquid, season it, if desired, and add the fillets to the skillet. Lower the heat so the liquid is at a simmer and put the lid in place. Once the fish is cooked, serve it immediately topped with some of the sauce, or remove the grouper, boil to reduce the liquid and add more ingredients, such as capers and lemon juice, before serving.