Divide the ready-made puff pastry in half, roll out each piece and cut into a 25cm round. Put one round on a baking sheet and spread with the apricot jam to within 2cm of the edges.
Beat together the softened butter and caster sugar until light and fluffy, then beat in the egg. Stir in the ground almonds and cognac or dark rum.
Spoon the mixture over the jam, spreading it evenly. Brush the edges of the pastry with water, then cover with the second piece, pressing the edges to seal. Mark the top of the pastry from the centre to the edges like the spokes of a wheel or in a zig zag pattern, then brush with beaten egg.
Bake for 25-30 mins until crisp and golden. Serve warm or cold.