Description
This delicious onion tart recipe features sweet caramelised red onions nestled in a creamy, cheesy custard filling on a crisp, homemade yogurt and milk-based pastry crust. Perfect for a light lunch or elegant appetizer, the tart combines rich Gruyère cheese with fragrant thyme and Dijon mustard for a flavorful and comforting dish that’s sure to impress.
Ingredients
Scale
Onion Filling
- 2 large red onions (550g / 1lb 4oz total), halved lengthways
- 2 tbsp rapeseed oil
- 1 tsp thyme leaves
- 1 tsp Dijon mustard
- 25g Gruyère cheese, grated
- Salt and freshly ground black pepper, to taste
Pastry Base
- 175g self-raising flour
- 25g cold butter, cut into small pieces
- 100g natural yogurt
- 4 tbsp semi-skimmed milk
- A pinch of salt
Custard Filling
- 2 medium eggs
- 200ml half-fat crème fraîche
Instructions
- Caramelise the onions: Slice the halved onions into thin, wedge-shaped pieces. Heat the rapeseed oil in a large, non-stick sauté or deep frying pan over medium heat. Add the onions and cook for about 20 minutes, stirring occasionally to allow them to caramelise evenly and become sticky and well browned underneath.
- Prepare the pastry dough: While the onions cook, preheat your oven to 190°C (170°C fan)/Gas Mark 5 and place a baking sheet inside to heat. In a bowl, combine the self-raising flour, salt, and cold butter. Rub together with your fingers until the mixture resembles coarse crumbs. Mix the natural yogurt and semi-skimmed milk together, then pour into the flour mixture. Using a knife, briefly work it all together until the dough just comes together. Be careful not to overwork. Gently press into a ball.
- Roll and line the tart tin: Lightly flour a surface and roll the dough out thinly. Line a 23cm round, fluted, loose-based flan tin, about 2.5cm deep, pressing the dough into the flutes with your fingers. If sticky, dust your fingers with flour. Place the lined tin on the hot baking sheet in the oven to warm slightly while you prepare the filling.
- Make the custard and assemble the tart: In a medium bowl, beat the eggs, then stir in the crème fraîche, thyme leaves, Dijon mustard, salt, and pepper to taste. Spoon half of the caramelised onions evenly over the pastry base and scatter over half of the grated Gruyère. Pour the egg and crème fraîche mixture over the onions and cheese evenly. Top with the remaining onions and Gruyère cheese.
- Bake the tart: Place the tart tin on the preheated baking sheet and bake in the oven for 25-30 minutes until the pastry base is cooked through and the filling is set and golden on top.
- Cool and serve: Remove the tart from the oven and let it cool in the tin for about 10 minutes. Carefully remove the tart from the tin and serve warm for best flavor and texture.
Notes
- Ensure onions caramelise slowly over medium heat to develop maximum sweetness and flavor.
- Do not overwork the dough to keep the pastry light and flaky.
- Use a loose-based flan tin for easy removal of the tart after baking.
- Letting the tart cool slightly helps the filling to set and makes it easier to slice.
- This tart is delicious served warm with a side salad for a complete meal.
- Prep Time: 25 minutes
- Cook Time: 30 minutes
- Category: Tart
- Method: Baking
- Cuisine: French
Keywords: onion tart, caramelised onion tart, savory tart, vegetarian tart, Gruyère cheese tart, homemade pastry, French tart recipe
