Place 2-3 apples in a small pan with a dash of water, cover and cook over a low heat until soft. Mash gently or purée if preferred. Allow to cool.
Unroll the 375g puff pastry sheet and spread the cooked apple and 300g leftover mincemeat over the top leaving a 3cm border along one of the long edges (this is to prevent the filling from escaping).
Tightly roll up the pastry along the long edge.
Chill in the fridge for 30 minutes.
Pre-heat the oven to 180°C (fan)/200°C/gas mark 6 and line a baking tray with non-stick baking paper.
Remove the pastry from the fridge and cut into 9-10 slices with a sharp knife. Place flat on the baking tray.
Bake in the oven for 15-20 minutes until the pastry has turned golden brown.
Remove from the oven and either serve warm or allow to cool on a wire rack.
Store in an airtight container.