Place all but the last 3 ingredients in a large jug and whisk into a smooth batter. Set aside for 1 hour, or until the batter has increased in volume and is incredibly bubbly, looking a bit like a science experiment.
When ready, place the baking powder in a small bowl, stir in the cold water, then mix briefly into the batter.
Lightly grease a large frying pan, preferably cast iron, and lightly grease 4 x 10cm rings. You can use tart rings, crumpet rings or any form of dessert ring, but you can also do without the rings, cooking the batter like pancakes. In this form, they are known as ‘pikelets’.
Place the greased rings in the pan over a low–medium heat. Divide the batter evenly between them and allow to cook until the bubbles that appear on the surface hold their shape and the batter starts to dry out and lose its shine. When almost set and the base of each crumpet is browned, flip them over and cook for another minute or so, until browned. Serve while still warm, or let them cool completely and serve later, toasted until crisp. These are best eaten on the day they are made, spread with salted butter and honey or jam.