Preheat the oven to 200 °C (180 °C fan). Peel the red onions, cut them into thin strips and pick the thyme leaves.
Gently heat the olive oil in a frying pan and fry the red onions slowly until soft and translucent. Add the maple syrup, balsamic vinegar and thyme and let it reduce briefly.
Lay the fresh puff pastry on a baking tray lined with baking paper and fold the edges in slightly. Prick the middle several times with a fork.
Spread the onion mixture over the puff pastry and dot the soft goat's cheese on top in small pieces. Beat the egg and brush the edges with it.
Bake the tart at 200 °C for 20–25 min, until the puff pastry is golden brown and crisp and the goat's cheese has taken on a little colour.
Let it cool briefly, then serve warm. Finish with a little fresh thyme and a few drops of olive oil if you like.
Good to know
This tart is simple and still a little special. Sweet, savoury and tangy notes meet here quite calmly. Just right when you want little effort to taste like a bit more.
Swaps
Puff pastry → spelt puff pastry (a little more fibre) | soft goat's cheese → sheep's milk feta (more protein, stronger flavour) | maple syrup → date syrup (more minerals, stronger sweetness) | egg → a little olive oil for brushing (no egg, with monounsaturated fats instead)
Allergens
Contains gluten, egg and milk. Usually well suited to children if the onions are gently braised; during pregnancy, only make it with goat's cheese made from pasteurised milk.