Boil double cream and caster sugar slowly in a pan for 3 minutes.
Cool the mixture, then whisk in lemon juice and zest.
Pour into glasses and refrigerate for 3 hours.
Preheat the oven to 180°C.
Sift icing sugar, plain flour, cornflour, and ground almonds into a bowl.
Pulse the mixture in a food processor with butter until smooth.
Add almond essence and pulse into a smooth dough.
Grease a muffin tray with butter.
Roll dough into balls and flatten slightly in the muffin cups.
Bake for 8 to 12 minutes until light golden.
Make a small indentation in each warm biscuit with your thumb.
Cool for a few minutes before removing from the tray.
Dust the cooled shortbreads with icing sugar.
Fill the biscuit indentations with lemon curd.
Serve the possets on plates with shortbread biscuits alongside.