Sift flour and bran, rub in butter to resemble breadcrumbs. Add enough water to mix to a firm pliable dough. Refridgerate while preparing filling.
Roll half the pastry to cover base and side of an 20cm pie plate, spread evenly with filling, cover with remaining pastry. Brush edges with water, pinch together, brush top with water. Make several cuts in pastry to allow steam to escape.
Bake in a moderately hot oven for 10 mins, reduce to moderate, bake for further 20-30 minutes, or until well browned.
Remove white stalks from spinach, slice leaves finely, combine with onion, feta and cheddar cheese, eggs and pepper, mix well.