In a food processor or by hand, mix the flour, baking powder, xanthan gum and salt together.
Add the butter and sugar. Process or rub in using your fingers until the mixture appears like coarse breadcrumbs.
Add the egg and lemon peel. Mix well and slowly add the ice-cold water until the dough comes together.
Place the dough on a sheet of baking paper and shape the dough into a log. Cut a third of the dough away and put it to one side. This will be used for the lattice covering of the pie.
With the larger piece of dough, flatten the dough into a disc using your hands. Cover with another sheet of baking paper or plastic wrap and begin to roll out the dough to 1 cm in thickness and into a circle large enough to fit the baking tin. This may seem thin, but the dough expands while baking.
Grease the springform tin lightly.
Lift the baking sheet and flip over the dough onto the baking tin. Some of the pastry may crack or tear, but this can easily be repaired by pressing and moulding the pastry in the tin.
Tidy up the edges of the pastry, making sure it runs evenly around the tin with at least 1 cm thickness and reaches 5 cm in height.
Place the baking tin in the fridge while the apple filling is prepared.