Heat your oven to 180°C/160°C Fan/355°F/Gas mark 4.
Place your large baking tray into your oven to heat.
Using your hand mixer, beat your butter a little to ensure a soft and spreadable in consistency. Add your caster (superfine) sugar and continue to beat on a medium-light setting until lighter in colour and soft and spreadable, this can take 1-2 minutes. Wipe your bowl down as you go with your spatula to ensure everything mixes evenly.
Add your egg and level tablespoons of flour and beat on low until fully incorporated, then beat in your almond extract. Again wipe down your bowl to ensure all of the mixture is incorporated.
Beat your frangipane batter for 10-15 seconds to ensure lots of air is beaten in.
Gently fold in your ground almonds. The mixture should then look a bit like curdled egg.
Cut off the base of a piping bag, about 2cm is enough, and then fill it with your frangipane mixture.
Pipe frangipane into each pastry case, I find it easiest to pipe a swirl around the outside and then finish in the middle. Ensure that you leave a gap of about 5 millimetres from the top of the pastry case, so it has room to rise.
Spread the frangipane out using a teaspoon, making sure that it completely covers the jam and there are no gaps between the batter and the sides of the tart, otherwise the jam will bubble through during baking.
Place your tartlets onto your heated baking tray and bake for 20 minutes until the frangipane is golden, has risen and has a domed shape and the pastry is just starting to get a little light brown in colour.
Remove from your oven and leave to cool for 5 minutes in the tartlet tins on the heated baking tray, this allows the base to continue to bake. Then gently press the frangipane down using the back of a spoon so that it flattens out.
Leave to cool for about 20 minutes until the tartlet tins are cool, then tip out of the tins and leave to fully cool on a cool rack.