Caramelized Onion Tart Recipe

Make dough

In a medium bowl, whisk together flour and 1/2 tsp salt. Cut cold cubed butter into the flour with a pastry cutter or your fingertips until mixture resembles coarse crumbs with some pea-sized pieces remaining.

Add water and chill

Sprinkle ice water, 1 tablespoon at a time, over the flour and gently toss until dough holds when pressed but not wet or sticky. Form into a disk, wrap in plastic, and chill in refrigerator for 30 minutes.

Roll and blind bake

Preheat oven to 375°F (190°C). On a lightly floured surface, roll chilled dough to about 1/8-inch thick and fit into a 9-inch tart pan with removable bottom. Trim edges, line with parchment and fill with pie weights or dried beans. Blind bake for 15 minutes, remove weights and parchment, then bake 5–7 minutes more until pale golden. Let cool slightly.

Cook onions

While dough chills (or while tart shell bakes), heat 2 tbsp olive oil and 1 tbsp butter in a large skillet over medium heat. Add the thinly sliced onions and 1/2 tsp salt and cook, stirring occasionally, until softened, about 10 minutes.

Caramelize

Reduce heat to medium-low. Continue to cook the onions, stirring every few minutes, allowing them to brown slowly. After about 25–30 minutes total cooking time the onions should be deep golden brown. Stir in 1/2 tsp sugar about halfway through to encourage caramelization, and add 1/4 tsp freshly ground black pepper. Stir in 1 tbsp fresh thyme leaves in the last 2 minutes of cooking. Remove from heat and let cool slightly.

Prepare cheese layer

In a small bowl, crumble the goat cheese and mix with grated Parmesan until smooth and spreadable. If too stiff, stir in 1–2 teaspoons of water or olive oil to reach a spreadable consistency.

Assemble tart

Spread the tapenade in an even layer over the bottom of the cooled prebaked tart shell (about 1/2 cup). Dollop or spread the goat cheese mixture over the tapenade in an even layer. Top with the caramelized onions, spreading them to cover the tart evenly.

Brush and bake

Brush the exposed tart edge lightly with the egg yolk (beat the yolk first) to encourage browning. Bake the assembled tart at 375°F (190°C) for 12–15 minutes, until warmed through and the crust is golden.

Finish and serve

Remove tart from oven and let rest 5 minutes. Drizzle 1 tbsp extra-virgin olive oil over the top, scatter 1 tbsp fresh thyme leaves, and sprinkle 1/2 tsp flaky sea salt. Slice and serve warm or at room temperature.