Caramelised Onion & Gruyère Tarte Tatin

Ingredients

• 1 egg null, beaten, for glazing
• salt and black pepper
• 6 large onions, peeled, halved through the root
• 1 tsp fresh thyme leaves
• 2 tbsp balsamic vinegar
• 1 tbsp soft brown sugar
• 50 g butter
• 2 tbsp olive oil
• 1 x 320g sheet ready-rolled puff pastry
• 120 g Gruyère cheese, coarsely grated
• green salad, to serve
• Crusty sourdough bread, to serve

Method

1. Heat the oven to 200°C/fan 180°C. Melt the butter with the olive oil in a large ovenproof frying pan (cast iron or stainless — you want the onions to grip and bronze) over medium-low heat until foaming.
2. Season the cut sides of the onions generously with salt and pepper, then sit them cut-side down in a single snug layer. Don't crowd them — if they're jostling for space, work in a bigger pan or do it in two passes. Crowded onions steam; spaced onions caramelise.
3. Leave them undisturbed for 20 minutes — no stirring, no fiddling. You're after deeply bronzed, sticky cut sides and a kitchen that smells sweet and almost jammy. If you peek under one at 15 minutes and it's pale, push the heat up a notch.
4. Splash in the balsamic vinegar — it'll hiss and lift all the sticky bits off the pan, which is exactly what you want. Scatter over the brown sugar and thyme leaves. Cook for another 5 minutes, swirling the pan occasionally, until the liquid turns syrupy and clings to the onions like a glaze. Taste the syrup at the edge of the pan — adjust salt and pepper now, not at the table.
5. Slide off the heat and let everything settle for a couple of minutes. Scatter the Gruyère generously between and over the onions, letting it tumble into every gap and pool against the hot pan.
6. Drape the puff pastry over the top, tucking the edges down inside the pan around the onions like a duvet — that tucked edge becomes the crisp rim once you flip it. Brush all over with the beaten egg.
7. Bake for 25–30 minutes, until the pastry is deeply golden, puffed and properly crisp. Pale pastry will go soggy under the onions — give it the full colour. Rest for 5 minutes; this is non-negotiable, or the caramel will run when you flip.
8. Place a large serving plate over the pan, and with a confident movement (and oven gloves), invert the whole thing. Lift the pan away to reveal the glossy onions on top. Scatter over the fresh thyme leaves and serve warm with the dressed green salad alongside, the mustard vinaigrette cutting through the richness.