Place the flours, xanthan gum, baking powder, bicarbonate of soda and butter in a food processor and whiz until the mixture resembles fine breadcrumbs, or rub in by hand in a large bowl. Stir in the sugar. Using the blade of a knife, stir in the egg and buttermilk until the mixture comes together.
Tip the dough out on to a surface dusted lightly with rice flour and gently press it down to a thickness of 2.5 cm (1 inch). Using a 5 cm (2 inch) cutter, cut out eight scones. Place on a lightly floured baking sheet, brush with a little buttermilk, then place in a preheated oven, 220°C (425°F), Gas Mark 7, for about 12 minutes until golden and risen. Remove the scones from the oven and transfer to a wire rack to cool.
Meanwhile, whisk the cream until it forms fairly firm peaks and fold the strawberries into it. Slice the scones in half and fill with the strawberry cream.