Rub the butter into the flour until it resembles breadcrumbs.
Stir in the paprika, English mustard powder, salt, and cheese. Kneed with 3-4 tablespoons of cold water. Knead until a soft smooth dough has formed.
Wrap the dough with cling film and refrigerate for 30 minutes.
Add to a pot the spinach, onions, nutmeg, and season with salt and pepper. Cook slowly on medium heat, covered.
Remove from the heat and allow to cool somewhat. Add the remaining ingredients (except one egg) and mix well.
Take the pastry out of the refrigerator and roll it out with a rolling pin. Line a 9” Pie dish with the pastry and decorate the edges with the end of a fork. Prick the pastry all over to allow even cooking.
Place the pie dish (with pastry) into the air fryer at 320 degrees F, air fryer setting, for 8-10 minutes remove when golden brown.
Spoon the filling into the pie dish on top of the pastry.
Beat the remaining egg and brush all over the top of the quiche.
Air Fry for another 10-15 minutes at 300 degrees F, air fryer setting.
Allow to cool (and set) before serving.