Description
This French onion tart features a buttery thyme-infused cheesy pastry filled with sweet, caramelised onions and a rich, creamy egg custard. Topped with a fresh rocket and sundried tomato salad, it’s a delicious savory tart perfect for lunch or a light dinner.
Ingredients
Scale
Pastry
- 200g plain flour, plus extra for dusting
- 100g cold butter, cubed, plus 25g
- 150g gruyère, comté or vegetarian Italian-style hard cheese, grated (divided: 50g for dough, rest for filling)
- Small handful of thyme, leaves picked (divided: 1 tbsp for dough, remaining for filling)
- 1 tsp salt
- Freshly ground black pepper
- 2–3 tbsp cold water
Caramelised Onion Filling
- 1 tbsp olive oil
- 3 large onions, finely sliced
- 2 tbsp white wine or sherry vinegar
- 1 tbsp sugar
- 2 brown anchovies, finely chopped (or 1 tsp olive tapenade or umami paste)
Custard and Assembly
- 2 large eggs
- 300ml double cream
- 1 tbsp extra virgin olive oil
- 2 tsp balsamic vinegar
- 2 sundried tomatoes, finely sliced
- 6–8 pitted black olives, thinly sliced
- 1 tsp capers
- A few handfuls of rocket
Instructions
- Prepare the pastry: Put the plain flour and 100g cubed cold butter into a food processor. Blitz until the mixture resembles fine breadcrumbs. Add 50g grated cheese, 1 tbsp thyme leaves, freshly ground black pepper, and 1 tsp salt. Blitz again briefly to combine. Add 2-3 tbsp cold water and pulse until the dough just comes together. Alternatively, rub the flour into butter by hand, then stir in the remaining ingredients with a knife. Wrap the dough in cling film and chill in the fridge for at least 40 minutes.
- Caramelise the onions: Heat 25g butter and 1 tbsp olive oil in a large frying pan over low to medium heat. Add the finely sliced onions and a pinch of salt. Cook gently, stirring often, for 40-50 minutes until the onions are sticky, golden, and very soft. If the onions start to catch, reduce heat and add a splash of water. Stir in 2 tbsp vinegar, 1 tbsp sugar, and the finely chopped anchovies (or alternative). Continue to cook, stirring, until the vinegar evaporates and anchovies dissolve. Remove from heat and set aside.
- Blind bake the pastry: Preheat oven to 190°C (170°C fan)/Gas Mark 5. Roll chilled pastry out on a lightly floured surface to about 3mm thickness. Line a 23cm tart tin with the pastry, trimming edges with slight overhang. Patch any holes if necessary. Line the tart case with scrunched and then flattened parchment paper and fill with baking beans. Bake for 15 minutes. Remove parchment and beans, then bake for another 5-8 minutes until pastry looks dry and cooked without raw spots.
- Make the filling: In a bowl, whisk together 2 large eggs, 300ml double cream, remaining thyme leaves, and the rest of the grated cheese. Season with a pinch of salt and black pepper. Stir the caramelised onions into the egg mixture.
- Fill and bake the tart: Trim the edges of the pastry with a serrated knife to neaten. Pour the onion and custard filling into the pastry case. Gently tap the tart on the work surface to release air bubbles. Bake the tart on the middle oven shelf for 25-30 minutes until the filling is lightly golden, set in the center but still with a slight wobble. Remove from the oven and let cool in the tin for 15-20 minutes.
- Prepare the salad: Whisk 1 tbsp extra virgin olive oil and 2 tsp balsamic vinegar together in a bowl. Toss in the sundried tomatoes, sliced black olives, capers, and rocket leaves. Serve the salad piled on top of the tart or alongside it.
- Serving and storage: Serve warm or cooled. For a chilled tart, allow to cool completely then refrigerate. The tart will keep in the fridge for up to 3 days.
Notes
- Use vegetarian Italian-style hard cheese if avoiding animal rennet.
- Patience is key for caramelising onions slowly to achieve the best flavor and texture.
- Anchovies add umami, but olive tapenade or umami paste can be substituted for a vegetarian option.
- Chilling the pastry well helps prevent shrinkage during baking.
- The slight wobble in the cooked filling ensures a creamy, custardy texture rather than overcooked dryness.
- Blind baking prevents the pastry from becoming soggy once filled with the moist custard and onions.
- Prep Time: 1 hour
- Cook Time: 1 hour 10 minutes
- Category: Savory Tart
- Method: Baking
- Cuisine: French
Keywords: French onion tart, caramelised onion tart, savory tart, thyme pastry, cheesy tart, vegetarian tart, French cuisine
