Preheat your oven to 160°C/140°C Fan/Gas Mark 3, then lightly grease a 23cm loose-bottomed flan tin.
Open out the pastry sheet onto a flour-dusted work surface then roll it out until roughly 27cm in length.
Lift the pastry over the prepared flan tin (with your rolling pin) then press the pastry gently onto the base and sides. Trim off any excess pastry with a knife then refrigerate for 15 minutes to rest.
Cream the caster sugar and butter together until pale and fluffy then beat in the eggs, one at a time, until the mixture is smooth.
Stir in the almonds and cornflour.
Spread the jam over the pastry base, top with the almond mixture then smooth level.
Arrange the apricots over the top, pressing them down a little then bake for 1 hour until a skewer comes out clean.
Remove from the oven and allow to cool in the tin for 15 minutes.
Slice then serve warm or leave in the tin to cool competely. Sprinkle with icing sugar to serve.