Caramelize the onions

• Heat the olive oil and a little butter in a frying pan over medium-low heat.
• Add the sliced onions with a pinch of salt and cook slowly, stirring often, until soft and deep golden.
• Stir in the brown sugar and cook a few more minutes until jammy.

Make the garlic butter

• Mix the remaining softened butter with the minced garlic and grated parmesan.
• Season lightly with salt.

Assemble the bread

• Spread the garlic butter over the cut sides of the baguette halves.
• Top with the caramelized onions, then the grated mozzarella.

Bake

• Bake at 200 °C until the cheese is melted and bubbling and the edges are crisp.
• Finish with chopped parsley and serve hot.