Ingredients:

  • 2 large yellow onions, thinly sliced (approximately 400g)
  • 2 tablespoons olive oil (30ml)
  • 1 tablespoon unsalted butter (15g)
  • 1 teaspoon granulated sugar (5g)
  • 1/2 teaspoon salt (2.5g)
  • 1/4 teaspoon black pepper (1.25g)
  • 2 tablespoons dry white wine (30ml), optional
  • 1 sheet Pillsbury Puff Pastry, thawed (approximately 397g)
  • 4 ounces Gruyère cheese, grated (approximately 113g)
  • 1 large egg, beaten (for egg wash)
  • 1 tablespoon fresh thyme leaves, chopped (approximately 3g), optional
  • 1/4 cup balsamic vinegar (60ml)

Instructions:

  1. Sauté onions in olive oil and butter until softened. Add sugar, salt, and pepper. Cook over low heat, stirring frequently, until deeply golden brown and caramelized. Deglaze with white wine (optional). Cool slightly.
  2. Unfold thawed pillsbury puff pastry sheet on a lightly floured surface. Cut into 6 equal squares.
  3. Gently press each puff pastry square into a tartlet tin or muffin tin. Prick the bottom with a fork.
  4. Sprinkle grated Gruyère cheese into each tartlet shell. Top with caramelized onions.
  5. Brush the edges of the puff pastry with egg wash. Bake in a preheated oven until golden brown and puffed up.
  6. Simmer balsamic vinegar in a small saucepan until reduced by half and thickened.
  7. Drizzle baked tartlets with balsamic glaze (optional) and sprinkle with fresh thyme (optional). Serve warm.