Halibut with Grapefruit Beurre Blanc

INGREDIENTS

• For beurre blanc
• 3 grapefruit (preferably 2 white and 1 pink or red)
• 1/4 cup dry white wine
• 1 shallot, minced
• 2 tablespoons white-wine vinegar
• 1 1/4 sticks (1/2 cup plus 2 tablespoons) unsalted butter, cut into tablespoon pieces
• For fish and vegetables
• 4 (1/2-inch-thick) halibut steaks with skin (1 1/2 lb)
• 3 tablespoons vegetable oil
• 1 lb fresh shiitake mushrooms, stems discarded and caps thinly sliced
• 2 Belgian endives, trimmed and cut crosswise into 1-inch-thick slices