Tip the onions into a large pan with 250ml water and a large pinch of salt. Cook over a high heat for 20 mins until the water has evaporated. Pour in the oil, turn down the heat to medium and cook for 20 mins more until the onions have caramelised. Pour in the vinegar and sugar and cook until the onions are jammy. Leave to cool.

Heat the oven to 190C/170C fan/gas 5. Roll the pastry out on a lightly floured work surface to a 30 x 40cm rectangle. Cut out six circles large enough to line six 10cm loose- bottomed fluted tart tins. Line each with a square of baking parchment, fill with baking beans and bake for 8 mins. Remove the parchment and beans and baking for 7 mins more. Leave to cool on a wire rack.

Remove the tart cases from the tins. Spread a layer of the onion jam in the bottom of each, top with the goat’s cheese slices, then sprinkle with pine nuts. Wrap each tart well and freeze for up to three months.

Heat the oven to 160C/ 140C fan/ gas 3, unwrap the tarts and bake from frozen on a baking tray for 15-20 mins until piping hot and the cheese has melted. Sprinkle with basil before serving.