Place the gramma in a saucepan with a little water and simmer, covered, for 45 minutes. Drain and let cool, then press lightly into a sieve to extract as much of the liquid as possible.
Place the gramma into a bowl, add sugar, the juice and rind of the lemon. Add sultanas, golden syrup and mixed spice. Refrigerate until pie base is made.
Preheat the oven to 200 C / Gas 6.
Fill the pastry lined pie plate with the gramma mixture, wet the edges then place the top pastry on. Trim excess and press edges with a fork to seal. Brush with milk and sprinkle a with a little extra sugar
Bake for approximately 1 hour, or until golden and filling is cooked through.