Preheat the oven to 180 C / Gas 4. Grease and lightly dust with flour a 23cm quiche dish or tart tin.
Roll out the pastry on a lightly floured work surface then transfer to the prepared tart tin and gently press into the base and sides. Trim any excess pastry and pinch the edges. Brush the pastry case with the mustard.
In a bowl, mix the beaten egg and single cream. Add grated courgette, grated cheese reserving a tablespoon of cheese for later, then season with salt, pepper and nutmeg.
Chop half of the pancetta slices and arrange the remaining slices over pastry case. Pour courgette mixture into case and even it out. Sprinkle with chopped pancetta and the rest of the grated cheese.
Bake in preheated oven for 30 minutes, or until centre is set and is slightly golden. Remove from the oven and serve warm, or allow to cool before serving.