1. One day before serving, marinate the fish: place the monkfish in a dish and pour the olive oil over it. Cover with the herbs and garlic. Cover the dish with plastic wrap and refrigerate overnight.

2. For the vegetables, preheat the oven to 550 degrees. Sprinkle both sides of the portobellos generously with salt and pepper. Put them in a roasting pan and scatter the thyme and garlic over them. Drizzle with 3 tablespoons of olive oil. Roast until the mushrooms are soft, sliding a spatula underneath them from time to time, about 12 minutes. Quarter the mushrooms and set them aside.

3. Meanwhile, bring a pot of salted water to a boil. Cut off the asparagus tips and reserve the stalks for another use. Blanch the tips until just tender, about 1¼ minutes. Drain and refresh under cold running water. Drain again and set aside.

4. Heat 1 tablespoon of olive oil in a 10-inch nonstick skillet over high heat. Add half the tomato slices in a single layer. Sauté until the slices are browned on the bottom, about 2 minutes. Turn and brown the other side, about 1 minute more. Set the tomatoes aside and wipe out the skillet. Add the remaining tablespoon of oil and Sauté the remaining tomatoes. Season with salt and pepper and set aside. (The vegetables can be made up to 1 day ahead; cover and refrigerate.)

5. For the sauce, heat the com oil in a medium saucepan over high heat. Add the beef and brown it on all sides, about 2 minutes. Pour off the fat. Add the brandy and deglaze the pan, scraping up any bits from the bottom. Add 2 tablespoons of butter and lower the heat to medium. Add the green peppercorns, cream, and demi-glace. Season with salt and pepper, if needed, depending on the spiciness of the peppercorns. Simmer for 8 minutes. Whisk in the remaining 2 tablespoons of butter, and simmer until the sauce is thick, about 7 minutes longer. Remove and discard the beef. (The sauce can be made up to 2 hours ahead; refrigerate.)

6. Start a large charcoal fire or preheat an indoor grill. When very hot, place the slate on the grill. Heat the slate until very hot, about 30 minutes. Preheat the oven to 450 degrees. Season the monkfish on both sides with salt and pepper. Pour half the oil from the marinade over the slate and lay the monkfish on top. Place the herbs and garlic back over the fish. After a few minutes, run a spatula under the fish to prevent it from sticking.

7. Grill until the fish is well browned on the bottom, about 10 minutes. Pour the remaining oil from the marinade on the slate, turn the fish over, and put the herbs and garlic back on top. Grill for 10 to 12 minutes, until a metal skewer can be easily inserted into the fish and feels hot when touched to your lip.

8. Meanwhile, alternate pieces of portobello and tomato in a ring around the platter, leaving room in the center for the fish. Lay the asparagus tips over the mushrooms and tomatoes. Place the platter in the oven just to reheat the vegetables, about 2 minutes. Reheat the sauce.

9. Place the monkfish in the center of the platter, covered with the herbs. Serve immediately, carving the fish at the table into ½-inch-wide slices. Pass the sauce separately. Leave the slate on the grill until cool enough to handle.