Line 2 baking sheets with nonstick baking paper.
Place the polenta, flour, ground almonds, baking powder, icing sugar and butter in a food processor and whizz until the mixture resembles fine breadcrumbs. Alternatively, mix together the polenta, flour, ground almonds, baking powder and icing sugar in a large bowl. Add the butter and rub in with the fingertips until the mixture resembles fine breadcrumbs.
Add the egg yolk and orange rind and combine to form a firm dough. Wrap in clingfilm and chill for 30 minutes.
Turn the dough out on a surface lightly dusted with rice flour, roll out thinly and use a 4 cm (1½ inch) cutter to cut out 20 cookies, rerolling the trimmings as necessary. Transfer to the prepared baking sheets and sprinkle with the flaked almonds.
Place in a preheated oven, 180°C (350°F), Gas Mark 4, for about 8 minutes until golden. Remove from the oven, leave for a few minutes to harden on the baking sheets, then transfer to a wire rack to cool.