All you do is sift the flour into a large mixing bowl, add the watercress, two-thirds of the cheese, the spring onions and 1 teaspoon of salt. Then, thinly pare off the potato skin using a potato peeler and, using the coarse side of a grater, grate the potato straight into the flour.
Now, using a palette knife, give everything a really good mix. Beat the egg and milk together and gradually add it all to the mixture until you have a loose, rough dough. Now transfer it to the baking tray and, still keeping the rough texture, pat it gently into a 6 inch (15 cm) round with your hands. Next, lightly press the rest of the cheese over the surface, sprinkle with a little flour and bake the bread on the middle shelf of the oven for 45-50 minutes, or until golden-brown.
Cool on a wire rack. Serve warm with Watercress and Buttermilk Vichyssoise.
To make this recipe gluten-free: This recipe also works well using gluten-free self-raising white flour. Or use plain gluten-free flour and simply add 11/2 teaspoons of gluten-free baking powder when you sift the flour
Pre-heat the oven to gas mark 5, 375, (190 C).
You will also need a small, solid baking tray, very well greased.