In a food processor, pulse the salmon, soft cheese, dill and a little seasoning until just combined. Unroll a sheet of puff pastry and cut into 3 pieces lengthways. Divide the filling along the middle of each piece, brush borders with beaten egg, then fold up and seal.
Cut each roll into 8-10 bite-size pieces, then place on a baking tray lined with baking parchment, cover with cling film and freeze. To serve, glaze with beaten egg and cook at 200C/180C fan/gas 6 for 25-30 mins until puffed and golden.
This canapé can be frozen for up to 3 months. If you're short on baking trays, then once the canapés are frozen solid, transfer them to freezer bags. Make sure they are well wrapped or sealed to preserve them properly. Label everything clearly to remind yourself what you've frozen.