Mix the mincemeat, nuts, cinnamon and maple syrup together; set aside. Lightly flour a work surface, then roll pastry out to a rectangle measuring 40 x 30cm. Trim the edges with a sharp knife.
Carefully position the pastry with one of the long edges facing you. Spread two-thirds of the mincemeat mix over the pastry, then fold the two shorter edges over to meet in the middle. Spread the rest of the mincemeat over the folded pastry and bring the outside ends over again to join in the centre. Turn the pastry over, lift onto a non-stick baking sheet, then gently squeeze down the length to make an even-shaped log, with tight folds. Chill in the freezer for 10 mins. Heat oven to 220C/fan 200C/gas 7.
Remove the baking sheet from the freezer. Cut the pastry into 1cm slices and arrange on baking sheets, spaced apart. Cook on the top shelf for 15 mins until risen and golden brown. Cool on a wire rack and serve dusted with icing sugar.
Making aheadWrap the filled pastry in cling film and freeze for up to 1 month. Slice while still frozen and bake at the same temperature for an extra 5-10 mins.
Making for veggies?Make sure you use vegetarian mincemeat.