Puy lentil, caramelised onion and thyme tart

Serves - 4

You’ll need

• 1 sheet all-butter puff pastry
• 2 large onions, finely sliced
• 2 tbsp olive oil
• 25g butter
• 1 tsp thyme leaves
• 1 x 250g pouch cooked Puy lentils, or 1 x 400g tin lentils, drained well
• 2 tbsp crème fraîche
• 1 tsp Dijon mustard
• 75g Gruyère, Comté or vegetarian hard cheese, finely grated
• 1 egg, beaten
• Sea salt
• Black pepper

Method

1. Get the onions going

Heat the olive oil and butter in a large frying pan over a medium-low heat. Add the sliced onions with a good pinch of salt and cook gently for 20–25 minutes, stirring now and then, until soft, golden and properly collapsed. This is not the part to rush. You want sweetness and depth, not onions that have simply warmed through and called it a day.

2. Add the thyme and lentils

Stir in the thyme leaves and cook for another minute until fragrant. Add the Puy lentils and give everything a good mix so they warm through and pick up all that oniony richness. Season with black pepper and a little more salt if needed, then take the pan off the heat and leave it to cool slightly.

3. Get the pastry ready

Heat the oven to 200°C fan. Unroll the puff pastry onto a lined baking tray and score a border about 2cm in from the edge, being careful not to cut all the way through. This is what gives you that nicely puffed edge rather than something flat and slightly sorry for itself.

4. Build the base

Mix the crème fraîche with the Dijon mustard, then spread it over the middle of the pastry, staying within the border. Scatter over half the grated cheese, then spoon the lentil and onion mixture evenly over the top. Finish with the rest of the cheese.

5. Bake until golden

Brush the pastry border with the beaten egg, then bake for 25–30 minutes until the pastry is puffed and bronzed and the topping is golden in places. You want crisp edges and a tart that looks as though it knows exactly what it is doing.

6. Serve

Leave the tart to sit for 5 minutes before slicing. Serve warm, ideally with a sharp green salad alongside to keep everything feeling nicely balanced. It is just as welcome at room temperature too, which makes it a useful one for lunch the next day.

A couple of helpful notes
- Puy lentils are especially good here because they hold their shape and bring a slightly nutty bite, but well-drained green lentils will also do the job nicely.
- If the onions look as though they are catching too quickly, turn the heat down and add a tiny splash of water rather than pretending they will sort themselves out.
- A little extra thyme scattered over the tart just before serving would not hurt at all if you want to push that flavour a touch further.