Preheat the oven to gas 6, 200°C, fan 180°C. Lightly flour a surface and roll out the pastry thinly. Using a 8cm (31⁄2in) fluted cutter, cut out 12 rounds and press into a greased 12-hole bun tin. Prick with a fork and chill for 10 mins.
Line each pastry case with a small piece of kitchen foil (allow a slight overhang to help you remove it later) and fill with baking beans. Blind bake for 10 minutes, until just turning golden and firm to touch. Remove the foil and baking beans and bake for another 3 minutes or until golden and crisp. Turn down the oven to gas 4, 180°C, fan 160°C.
For the frangipane filling, mix together the butter, sugar, egg, ground almonds and almond extract. Put 1 tsp of jam in each tart case and then divide the frangipane mixture between the cases. Smooth the top of each tart with a knife and then scatter with flaked almonds.
Bake for 18-20minutes, or until the frangipane is just set and golden. Remove from the oven and transfer to a wire rack, to cool.
Mix the icing sugar with a little water to make a runny icing. Drizzle over the tarts in a zigzag pattern and leave to set. Serve warm, if you like, or allow to cool.