Pre-heat the oven to 200°C. Grease and line a large baking tray with nonstick baking paper.
Roll the pastry out on a lightly floured surface to 1cm thickness. Cut 4 even rounds of pastry roughly 10cm in diameter and cut 4 star shapes as well using the remaining pastry. Use a sharp knife to cut out an inner circle from the pastry rounds, leaving a 2cm wide outer rim; this outer rim of pastry will form the nest.
Place all the pastry carefully on the lined baking tray and chill for 30 minutes.
Meanwhile, prepare the filling by creaming together the butter and sugar using an electric hand held whisk until pale and fluffy. Gradually beat in the egg, mixing really well. Fold in the ground almonds and set to one side.
Remove the pasty from the fridge and remove the inner pastry circles from the baking tray. Brush the outer rims and the stars with some of the beaten egg. Cook the pastry rims and stars for 10 minutes until risen and golden-brown on top, then remove.
Meanwhile, spread the filling thinly and evenly on top of the inner circles. Transfer to a lined baking sheet and bake for 6-8 minutes. Remove and assemble the tarts by sitting the the outer pastry circles on top of the inner circles.
Place a star-shaped pastry inside the tart on top of the filling and dust the whole tart with a little caster sugar before serving.