Place the flour, butter and sugar into the Thermomix bowl and mix for 10 sec/speed 6.
Add the chilled water and knead for 1 minute/dough setting. The pastry should now have come together, if not knead for a little longer.
Turn the pastry out onto a lightly floured surface and knead gently it into a ball then press down into a disc shape. Wrap in cling film and place in the fridge to rest for 15 minutes.
Preheat the oven to 180°C/350°F (160°C fan). Lightly grease a 12-hole patty tin.
Roll the pastry dough out between two sheets of baking paper until it is about 3mm thick. Using a round cutter, cut 12 bases and press them gently into the patty tin. Roll out the remaining pastry and cut out 12 heart shapes with a small heart-shaped cutter.
Spoon 2 teaspoons of jam into each pastry case, then top with the heart shape.
Bake in the oven for 15-18 minutesuntil the pastry is golden and the jam is bubbling.
Leave to cool in the tin for 10 minutes then enjoy warm or cold.
Notes
Jam tart tips: Ensure the butter and water for the pastry are well chilled - this keeps the pastry light, flaky, and easier to handle.Rolling the pastry - if it starts to soften while rolling, pop it back in the fridge for a few minutes.Avoid overfilling - too much jam can bubble over.Storage: Store the jam tarts in an airtight container at room temperature for up to 5 days. If it is hot where you are, store them in the fridge.To freeze: Cooked jam tarts can be frozen for up to 3 months. Cool completely before placing in an airtight container. Reheat in the oven at 160°C for 5-10 minutes or the microwave for about 10 seconds, until just warm.