Heat your oven to 200°C (400°F).

Heat the olive oil and butter in a large oven-safe frying pan (about 24cm/9in) over medium heat. We used a cast iron skillet.

Add the sliced red onions with a pinch of salt and cook gently for 8–10 min until soft and starting to caramelise.

Stir in the brown sugar and cook for another 1–2 min until it dissolves.

Add the balsamic vinegar, stir, and let it bubble down slightly. Remove the pan from the heat.

Nestle whole cherry tomatoes snugly into the onions.

Season with a little salt and pepper.

Roll out the pastry until it’s about 1cm larger than the skillet.

Lay it over the tomatoes and onions, tucking the edges down inside the pan to fully encase the filling.

Score a couple of slits into the pastry to allow the steam to escape.

Brush the pastry lightly with olive oil (or egg wash).

Place the tarte tatin in the oven for 25–30 min until the pastry is golden and puffed.

Let the tarte tatin rest for 5 min, then run a knife around the edges.

Place a large plate over the pan and carefully flip it over (mind the hot juices!).

Scatter with feta if desired, and serve warm.