Caramelised Onion Tart

Ingredients

Instructions

1. 1

   Preheat the oven to 200C. Lightly flour the work surface, roll the all-butter shortcrust pastry to about 3 mm thick, and line a 20 cm tart tin. Press it neatly into the corners without stretching, then trim the excess. Chill for 10 minutes so the pastry holds its shape in the oven.

2. 2

   While the pastry chills, melt the butter with the olive oil in a wide frying pan over medium heat. Add the sliced onions, sugar, thyme leaves, salt, and pepper. Cook for 18-20 minutes, stirring often, until the onions collapse, turn deep golden brown, and taste sweet rather than sharp. If they start catching, lower the heat and stir more frequently; proper caramelisation should be rich and jammy, not burnt.

3. 3

   Prick the chilled pastry base lightly with a fork. Bake for 12 minutes until the edges are just starting to colour and the base looks dry. This quick blind-free bake works because the tart is small, but the shell should look set before filling.

4. 4

   Whisk together the egg, double cream, and Dijon mustard until smooth. Stir in half of the grated Gruyere to help the custard bind and add savoury depth.

5. 5

   Spread the caramelised onions evenly over the hot pastry shell. Pour over the custard, then scatter the remaining Gruyere and the extra thyme leaves on top. Keep the filling level just below the rim to avoid spills.

6. 6

   Return the tart to the oven and bake for 16-18 minutes until the custard is just set, the cheese is melted, and the top is golden in patches. The centre should have only a slight wobble when gently shaken.

7. 7

   Rest the tart for 5 minutes before removing it from the tin and slicing. Serve warm, when the filling is set but still soft and creamy.

Nutrition per serving

Notes

• •A 20 cm tart tin gives a neat tart for 2 generous servings.
• •If using shop-bought pastry straight from the fridge, let it soften for a few minutes so it rolls without cracking.
• •For deeper onion flavour, deglaze the pan with 1 tablespoon water during caramelising if browned bits build up too quickly.
• •This tart is excellent with a bitter leaf salad or lightly dressed watercress.

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