Mix the flour, sugar, baking powder, soda, xanthan gum and salt, very thoroughly.
Add the eggs and vanilla and use a stiff spoon to beat well. Finally add the cherries and the pistachios. Depending on the flour, add a drop more water if the mixture is dry; you want soft dough that holds its shape.
Flour your hands, divide the dough in half and shape into two equal rolls, roughly 30cm x 5cm (12″x 2″). Sprinkle with flour if the dough is sticky.
Place both dough rolls onto the baking sheet and brush well with the egg wash.
Bake in the oven for about 30 minutes until pale golden and set.
Remove the logs from the oven and place the baking sheet on a rack to cool slightly for about 10-15 minutes.
Transfer to a chopping board and slice into 1½ cm (¾″) slices.
Place back onto the baking sheet and re-bake for 15-20 minutes until golden and crisp.