On a lightly floured work surface, roll out the pastry to about 2mm thick. Cut out six 15cm circles and line your tartlet tins with them. Prick the bases with a fork, then chill for 30 minutes.
Preheat the oven to 200°C/Fan 180°C/Gas 6 and put in a baking sheet to heat up. Heat the oil in a frying pan over a medium heat, add the onion and cook for 8 minutes to soften, then remove and set aside to cool.
Whisk the whole egg and egg yolk with the cream and two-thirds of the Cheddar, then season well with salt and pepper and set aside. Mix the breadcrumbs with the tomato paste and remaining cheese and set aside.
Place a spoonful of chutney in the middle of each tart case, spoon the onions over the top, then pour over the egg filling. Thickly sprinkle with the breadcrumbs and Cheddar mixture and finally top with a whole cherry tomato, pressing it slightly into the filling.
Reduce the oven to 190°C/Fan 170°C/Gas 5 and place the tartlets in the oven on the hot baking sheet. Bake for 35-40 minutes until the filling has set and the top is crispy and golden. Cool slightly, then turn out of the tins and serve with a crisp salad