French Caramelised Onion Tart
mainsIntermediate

French Caramelised Onion Tart

A classic of the French bistro — a buttery shortcrust shell filled with deeply caramelised onions, a silky egg and cream custard, and melted Gruyère, baked until just set with a golden wobble.

1 hr 30 min8 servings

Ingredients

  • For the pastry: 200 g plain flour, 100 g cold unsalted butter (cubed), 1 egg yolk, 2–3 tbsp ice-cold water, pinch of salt
  • For the filling: 1 kg yellow onions, very thinly sliced, 3 tbsp unsalted butter, 1 tbsp olive oil, 1 tsp fresh thyme leaves, 1 tsp caster sugar, 1 tbsp dry white wine or sherry
  • For the custard: 3 large eggs, 200 ml double cream, 100 ml whole milk, pinch of freshly grated nutmeg, salt and white pepper
  • 100 g Gruyère, coarsely grated
French Caramelised Onion Tart

Instructions

  1. 1

    Make the pastry: pulse the flour, butter, and salt in a food processor until the mixture resembles breadcrumbs. Add the egg yolk and water and pulse until the dough just comes together. Flatten into a disc, wrap, and refrigerate for 30 minutes.

  2. 2

    Caramelise the onions: melt the butter and oil in a wide, heavy pan over medium-low heat. Add the onions, thyme, and a pinch of salt. Cook, stirring every 5 minutes, for 45–55 minutes until the onions are a deep, jammy amber. Add the sugar and wine in the last 5 minutes. Cool.

  3. 3

    Preheat the oven to 190°C (375°F). Roll the pastry to 3 mm thick and line a 23 cm loose-bottomed tart tin. Prick the base, line with baking paper and weights, and blind bake for 15 minutes. Remove the weights and bake for a further 5 minutes until the base is dry and pale golden.

  4. 4

    Whisk the eggs, cream, milk, nutmeg, salt, and white pepper together until smooth.

  5. 5

    Scatter half the Gruyère over the tart base. Spread the caramelised onions evenly on top. Pour the custard over slowly — it should come to just below the rim.

  6. 6

    Scatter the remaining Gruyère over the surface. Bake for 25–30 minutes until the custard is just set with a slight wobble in the centre and the top is golden.

  7. 7

    Cool in the tin for 15 minutes before slicing — this allows the custard to firm up enough to cut cleanly. Serve warm or at room temperature with a simple green salad dressed with Dijon vinaigrette.

Frenchvegetariantartpastrybistro

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