Fancy Tuna Recipes: My Posh Tuna Melt with Gruyère

Ingredients

• 2 medium yellow onions, thinly sliced (approx. 300g / 10.5 oz)
• 2 tablespoons olive oil (30 ml)
• 1 tablespoon butter (15g / 0.5 oz), unsalted
• 1 tablespoon brown sugar (15g / 0.5 oz)
• 1/4 teaspoon salt (1.5g / 0.05 oz)
• 1/4 cup dry white wine or chicken broth (60 ml / 2 fl oz) optional
• 2 cans (5 oz/142g each) tuna in olive oil, drained well (approx. 284g / 10 oz)
• 1/4 cup mayonnaise (60g / 2 oz)
• 2 tablespoons finely chopped celery (30g / 1 oz)
• 1 tablespoon finely chopped red onion (15g / 0.5 oz)
• 1 tablespoon lemon juice (15 ml / 0.5 fl oz)
• 1/2 teaspoon Dijon mustard (3g / 0.1 oz)
• 1/4 teaspoon black pepper (1.5g / 0.05 oz)
• Pinch of red pepper flakes (optional)
• 1 clove garlic, minced (3g / 0.1 oz)
• 1 teaspoon lemon zest (3g / 0.1 oz)
• 1/2 teaspoon lemon juice (2.5 ml / 0.1 fl oz)
• 4 slices sourdough bread
• 4 ounces (115g / 4 oz) Gruyère cheese, grated
• 2 tablespoons butter, softened (30g / 1 oz)