Cider-cooked apple, onion and cheese galette

Method

1. For the pastry, put the plain flour, cornmeal/polenta and salt in a large mixing bowl and stir to combine. Grate in the frozen butter, using the foil to hold it, then flick the flour over the butter using a dinner knife. Slowly add the iced water, stirring with the knife to combine; stop adding water just as it starts to come together (you may not need it all). Tip the pastry out onto a lightly floured work surface and bring it together quickly with your hands into a fat disc. Handle the pastry as little as possible, to keep it cool and stop the butter melting. Wrap in cling film, then chill for at least 2 hours.
2. For the filling, melt the butter in a large sauté/frying pan over a medium-high heat, add the onions and season well with salt. Fry for about 30 minutes, stirring often, until the onions are soft, lightly golden and slightly caramelised.
3. Add the apples and the cider, turn up the heat and bubble for 15-20 minutes until the cider has evaporated. Tip the mixture onto a plate to help it cool, then season with pepper and leave to cool completely.
4. Heat the oven to 200°C/180°C fan/gas 6. Mix the cheeses, cayenne, mustard powder and chopped herbs in a bowl. Remove the chilled pastry from the fridge, unwrap, then roll it out on a very well floured surface to form a rough circle the thickness of a £1 coin. The edges can be ragged.
5. Lift the pastry onto a large baking sheet lined with baking paper, then pile the cooled filling onto the centre, leaving a rough 3cm border around the edge. Scatter most of the cheese over the onion mixture, then fold the edges of the pastry up around the filling. Brush the pastry with beaten egg, then scatter the remaining cheese on top. Bake for 30 minutes until the pastry is golden and the cheese is bubbling. Leave to cool for 5 minutes, then slice and serve with a sharp green salad.