- 4½ tablespoons butter, softened
- ¼ cup grainy mustard, like moutarde de Meaux
- ½ cup shelled, skinned, and toasted finely ground or minced hazelnuts
- Four 6- to 8-ounce bone-in halibut or other fish steaks, or 2 larger steaks, each at least 1 inch thick
- Salt and cayenne pepper
- 6 sprigs thyme
- 1½ cups dry white wine
- ½ cup small black olives, such as Niçoise, with pits
- Cream 3 tablespoons of the butter with the mustard and hazelnuts in a small bowl. Season the fish with salt and cayenne pepper and spread the butter mixture all over one side of each steak. Refrigerate for 1 hour if time allows.
- Preheat the oven to 500°F. Spread the remaining 1½ tablespoons butter in a shallow baking pan that will hold the fish without crowding. Place the fish in the pan, then top it with a couple of thyme sprigs. Pour the wine around the fish and scatter the olives around; strip the leaves from 4 sprigs of thyme and scatter them around as well.
- Bring to a boil on top of the stove, then transfer to the oven and cook for 10 to 12 minutes, undisturbed, until the fish is just about done; it should be firm and just about opaque nearly all the way through.
- Turn on the broiler and place the fish about 3 inches from the heat source. Broil for a minute or two, or until the crust is bubbly and light brown. Serve.