For the pastry, place the flours, almond meal, sugar, salt and nutmeg in a food processor and process until combined. Add the butter and process until the mixture resembles coarse breadcrumbs. Add the vinegar and half the water and continue to process until a dough forms – add more water if needed. Form the dough into a ball, wrap in plastic wrap and refrigerate for one hour.

Unwrap the dough, place on a floured surface and roll into roughly a 20x20-centimetre square. Don't worry if it's a bit crumbly, it will come together with the rolling. Fold the dough into thirds, roll out to a square again, then fold into thirds again. Repeat the process, then wrap the dough in plastic wrap and return to the fridge for at least one hour, preferably overnight.

When ready to cook, preheat oven to 180C.

For the filling, cut the leeks in half lengthways and wash any dirt from them. Cut or snap the bottom few centimetres off each asparagus spear and slice the stalks into small rounds, leaving a 3-cm tip. In a medium pan, heat the oil and butter over a low heat and cook leeks gently until soft and pale. Reserving the tips, add the asparagus rounds and cook briefly, about 2 minutes - they will keep cooking when the galette is baked.

Roll out the pastry to a rough 30-cm circle. Pour the filling into the centre and spread out, leaving a 5-centimetre gap around the edge. Lie the asparagus tips randomly over the filling. Fold the pastry over the filling, working your way around and crimping as you go. Brush the pastry with the beaten egg and bake for about 40 minutes or until it is crispy and golden.

Remove from the oven, place on a cooling rack, let cool slightly before eating and sprinkle with parmesan before serving.