Mix together the flours, starches, sugar, xanthan gum, salt, yeast and vitamin c in a large bowl
Mix the milk, oil and vinegar together and add to the flour mix
Form a soft dough then lightly grease a piece of cling wrap and cover the bowl
Let rise in a warm place for an hour
Punch the dough back down and add 3/4 of the seeds/walnut mix. Shape into a large ball and roll in the remaining seeds/walnut to coat
Place the dough onto a baking tray and shape into a round. Cover with another sheet of greased cling and leave in a warm place for another hour
When the hour is almost up, preheat the oven to gas 7 / 220C / 425°F
Remove the clingfilm and bake for 15 minutes, then reduce the oven temperature to gas 5 / 190C / 375°F and bake a further 30 minutes
The base should sound hollow when tapped. Let cool completely on a wire rack before cutting into slices
Keeps for 3 days in an airtight container or wrap each slice separately and freeze
