Red Onion Tarte Tatin

I love the quiet magic of turning simple ingredients into something that feels like a celebration, this savoury Red Onion Tarte Tatin is just the ticket. It’s a table centrepiece, a heartwarming crowd pleaser with minimal ingredients that reminds me of something you would get for lunch in a little French cafe with a red checkered tablecloth.

Swapping sweet apples for caramelised red onions, this tart brings out the deep, natural sweetness of the onions, enhanced by a touch of balsamic vinegar and the earthiness of fresh thyme. I make it for lunch, alongside a Leek version to a similar tune, and a Courgette and Ricotta Farinata as a gluten-free option, side-salad optional.

Ingredients

500g puff pastry (homemade or high-quality store-bought)

6 large red onions, peeled and sliced whole with a mandoline into circles

100g unsalted butter

3 tbsp olive oil

4 tbsp balsamic vinegar

2 tbsp soft brown sugar

A handful of fresh thyme sprigs

Sea salt and freshly ground black pepper

Plain flour, for dusting

Method

Prepare the Onions
In a large, flat bottomed ovenproof frying pan, melt the butter with the olive oil over medium heat. Add the red onion circles, layering them snugly to cover the base of the pan. Sprinkle over the brown sugar, drizzle with balsamic vinegar, and tuck the thyme sprigs among the onions. Season generously with sea salt and freshly ground black pepper.

Caramelize
Cook the onions gently for about 25-30 minutes, on a low heat with a lid covering the pan, this retains the steam and ensures the onions are soft and cooked through. They should become soft and caramelised, their natural sugars mingling with the balsamic to create a rich glaze. Try not to stir them too much, maintain the circles of the onions, this slow cooking is where the flavour develops, so take your time.

Preheat the Oven
While the onions are cooking, preheat your oven to 180°C . The scent of caramelising onions will start to fill the air—a sign of good things to come. It is also perfectly possible to cook the onions in the morning, let them cool and reheat in the oven while the pastry cooks at lunchtime.

Roll Out the Pastry
On a lightly floured surface, roll out the puff pastry to a circle slightly larger than your pan (about 30cm in diameter if using a standard pan). The pastry should be about 5mm thick. Using a fork, prick the pastry all over to prevent it from puffing excessively.

Assemble the Tart
Once the onions are tender and beautifully glazed, remove the pan from the heat. Carefully lay the pastry over the onions, tucking the edges down between the onions and the side of the pan. Work gently—you want to encase the onions snugly.

Bake
Place the pan in the preheated oven and bake for 25-30 minutes, or until the pastry is puffed up and golden brown. The anticipation builds as the pastry transforms, its edges crisping, promising flaky layers beneath.

Invert the Tart
Remove the tart from the oven and allow it to rest for 5 minutes. To invert, place a large serving plate over the pan. Using oven mitts (the caramel will be very hot), swiftly and carefully flip the pan over so the tart drops onto the plate, revealing the glossy, caramelized onions on top.

Garnish and Serve
Scatter a few fresh thyme leaves over the tart for a bright, herbal finish. Slice into generous wedges, I recommend using scissors, and serve warm. Perhaps pair it with a simple green salad, lightly dressed.