Melted Cheese and Chorizo with Grilled Bread

• 2 1/2 tablespoons grapeseed oil, or other neutral oil, divided
• 2 cups chopped white onions
• 1 cup (packed) thinly sliced leeks (about 2 small; white and pale green parts only)
• 1/2 cup dry white wine
• 8 ounces smoked Spanish chorizo, cut into 1/16-inch-thick rounds
• 3 cups coarsely grated Petit Basque cheese or Gruyère cheese

Grilled sourdough bread slices

1. Heat 1 1/2 tablespoons oil in large skillet over medium heat. Add onions; sauté until deep golden brown, stirring often and adjusting heat as needed to prevent burning, 25 to 30 minutes. Sprinkle with salt and pepper.
2. Meanwhile, heat remaining 1 tablespoon oil in medium skillet over medium heat. Add leeks; sauté 3 to 4 minutes. Add 3/4 cup water; cover and cook until leeks are tender, stirring often and adding more water by tablespoonfuls to moisten as needed, 10 to 15 minutes. Add wine; cook uncovered until leeks are very soft, about 5 minutes longer. Sprinkle with salt and pepper. Combine onions and leeks in small bowl.
3. Preheat oven to 450°F. Divide onion-leek mixture among 4 small gratin dishes. Top mixture in each dish with chorizo slices, then cheese.
4. Bake until cheese melts and bubbles, about 15 minutes. Serve hot with grilled bread.