Leek, Mushroom, and Gruyère Pasta (Rich Vegetarian Dinner Recipe)

Ingredients

• 2 tablespoons olive oil.
• 3 tablespoons butter divided.
• 3 medium leeks tops removed, cut in half and thinly sliced.
• ½ teaspoon salt.
• ½ teaspoon granulated sugar.
• ⅓ cup sherry wine.
• 8 ounces oyster mushrooms.
• 4 garlic cloves minced.
• 2 sage leaves.
• ¾ cup heavy cream.
• 1 tablespoon balsamic vinegar.
• 1 teaspoon lemon zest.
• 1 lb fettuccine.
• 1 cup reserved pasta water.
• ½ cup grated gruyere.
• 1 teaspoon black pepper.
• ¼ cup toasted pine nuts.