Onion & Prosciutto Tart

Soft, herbed onions and salty prosciutto spread over a sheet of puff pastry and baked until the edges puff up golden and shatteringly crisp. Sliced black olives go on toward the end, keeping their glossy bite against the sweet, melted onion filling.

Four large onions sounds like a lot, but they cook down dramatically. Sautéed slowly with thyme and rosemary until completely transparent, those onions lose their sharpness and turn jammy and sweet. The prosciutto goes in for just three minutes at the end so it stays distinct rather than disappearing into the onions.

Chilling the assembled tart for 30 minutes before baking is essential for puff pastry. Cold butter in the dough needs to hit a hot oven to create those flaky layers. If the pastry goes in warm, it’ll spread flat and turn dense instead of puffing. The egg wash on the raised borders gives them a deep golden shine.

Pro Tips

• Cook the onion filling and chill it completely before spreading it on the pastry. Warm filling will melt the butter in the puff pastry and ruin the rise.
• Cut the border strips from the same dough and press them firmly onto the edges. They create a raised frame that keeps the filling contained.
• Go easy on the salt. Prosciutto and olives are already quite salty, so taste the filling before adding any.
• Slice into small squares for appetizers or larger pieces as a main with a simple green salad.

Variations

• Goat cheese: Crumble goat cheese over the filling before baking for a creamy, tangy layer.
• Caramelized onion: Cook the onions longer over lower heat until deeply browned for an even sweeter, more intense tart.
• Anchovy: Replace the prosciutto with anchovy fillets for a classic pissaladiere-style tart.