Preheat the oven to 200°C/180°C fan/gas 6. Line a large baking tray with baking paper.
Put the sausage meat, apple, fennel, parsley and garlic into a large bowl. Using clean hands, mix until well combined.
Remove the pastry blocks from the packaging and cut each into 4 vertical strips, so you have 8 in total. Spoon the sausage meat down the middle of 4 of the strips, leaving a 1.5cm gap at either side.
Brush the edges with some of the beaten egg, then take the remaining pastry strips and lay them on top of the sausage meat, pressing down on each side to seal. Slice each into 8 sausage rolls, so that you have 32 in total.
Arrange the sausage rolls on the baking tray so that each one is standing up on one side, showing the filling on top, following the shape of a spiral. Brush all over with the remaining egg, then sprinkle over the fennel seeds.
Bake in the oven for 45-50 minutes until the pastry is crisp and the meat is cooked through. Allow to cool slightly before slicing to serve.
Make the dip by mixing the crème fraîche with the mustard and seasoning lightly. Serve with the sausage rolls.