Grate the Parmigiano Reggiano finely, and set aside.
Preheat the oven to 190°C / fan oven 170°C / Gas Mark 5. Put eight paper muffin cases into a muffin pan, or line them with squares of greaseproof paper.
Sift the flour, salt and baking powder into a large mixing bowl. Stir in the sugar, about two-thirds of the Parmigiano Reggiano and the spinach. In a large jug, beat together the egg, milk and vegetable oil.
Pour the liquid mixture into the dry ingredients. Using a metal spoon, stir until just combined. You must not beat this mixture or stir it too much. It should be quite lumpy, but there should be no traces of dry flour.
Spoon the mixture into the muffin cases and sprinkle the remaining Parmigiano Reggiano on top. Bake for 20-25 minutes until risen and golden. Serve whilst warm.
Cook’s tips: Press out the excess water from the cooked spinach with your hands or use the back of a spoon. If you’re wondering why sugar is in the recipe, this is because it improves the texture and flavour of the muffins.