Blueberry and polenta shortcake

Method

1. Heat the oven to 180°C/160°C fan/ gas 4. Grease a 23cm springform tin with a little butter and line the base with a disc of baking paper.
2. Put both flours and the butter into a food processor with a pinch of salt and whizz until it looks like fine breadcrumbs. Add the polenta, caster sugar and orange zest, then use the pulse button to mix briefly.
3. Combine the egg with the orange juice, add to the machine and pulse again briefly until the mix starts to come together in clumps. Tip the mix onto a dusted work surface and knead briefly to a dough.
4. Cut off 250g of the dough, wrap in cling film and rest in the fridge for 30 minutes. With lightly floured hands, press the rest of the dough onto the base of the prepared tin, working it 2cm up the sides.
5. Scatter the blueberries over the base of the shortbread and sprinkle with the 25g caster sugar and the polenta. Roll out the reserved piece of dough into a 23cm disc, lay it over the top of the berries and press the edges of the dough together to seal, then crimp with your fingers. Sprinkle over the demerara sugar.
6. Bake for 40-45 minutes until golden brown. Remove and cool in the tin for 20 minutes, then carefully unclip and transfer the shortcake to a serving plate or wire rack.