Heat the oven to 200C (180C fan)/390F/gas mark 6, and put the whole cherry tomatoes in a large bowl.
In a small bowl, whisk the balsamic vinegar with 30 ml of the oil, the maple syrup and a good pinch of salt, then pour over the tomatoes and toss to coat.
Dust a work surface with flour, then roll out the pastry to a 30 cm circle.
Leaving a border all around the edge, spread out the harissa in a 24 cm circle over the centre of the pastry.
Spoon the tomatoes and their dressing into a 24 cm oven-safe frying pan, lay the pastry harissa-side down on top, then tuck it in all around the edge of the tomatoes.
Bake for half an hour, until the pastry is cooked through and golden.
Once the pastry's cooked, remove the pan and leave it to cool for a few minutes.
Meanwhile, make a dressing by whisking the remaining extra-virgin oil with the lemon juice and mustard.
To serve, carefully invert the tarte tatin on to a large plate or board.
Dress the salad leaves and basil lightly, season with salt, and serve alongside.
