Halibut with Grapefruit Beurre Blanc

Preparation

1. Make beurre blanc:

   Step 1

   Finely grate 1 teaspoon zest from a grapefruit. Squeeze 1/2 cup juice from a white grapefruit.

   Step 2

   Cut peel, including all white pith, from remaining fruit with a sharp paring knife and cut segments free from membranes. Chop enough grapefruit segments (use all colors) to measure 1/2 cup. Reserve 1 cup of remaining whole segments.

   Step 3

   Boil juice, wine, shallot, and vinegar in a small heavy saucepan until reduced to about 1 tablespoon. Reduce heat to low and whisk in butter 1 piece at a time, lifting pan from heat occasionally to cool sauce and adding each new piece of butter before previous one has melted completely (sauce must not get hot enough to separate).

   Step 4

   Stir in chopped grapefruit and season with salt and pepper. Keep beurre blanc warm in a metal bowl set over a saucepan of hot water.

2. Cook fish and vegetables:

   Step 5

   Preheat oven to 250°F. Pat halibut dry and season with salt and pepper. Heat 1 1/2 tablespoons oil in a large nonstick skillet over moderately high heat until hot but not smoking, then sauté fish, in batches if necessary, turning over once, until golden brown and just cooked through, about 5 minutes total. Transfer fish to a shallow baking pan and keep warm in oven.

   Step 6

   Wipe skillet clean and heat remaining 1 1/2 tablespoons oil over moderately high heat until hot but not smoking, then sauté mushrooms with salt and pepper to taste, stirring, until golden brown, 5 to 7 minutes. Add endives and sauté, stirring, until leaves are slightly wilted, about 1 minute. Stir in reserved whole grapefruit segments and remove from heat.

   Step 7

   Serve fish over mushrooms, topped with beurre blanc and zest.