1. Sift the flour and salt into a bowl. Mix together the milk and hot water, add the sugar and stir to dissolve.
2. Sprinkle the yeast over the warm liquid and set aside for 10 minutes, until the mixture is frothy.
3. Add the yeast mixture to the flour and mix to a smooth batter, then beat hard for about 5 minutes with a wooden spoon or an electric mixer.
4. Cover the bowl with a damp cloth and leave in a warm place until the batter has doubled in volume – about 1 hour.
5. Dissolve the baking soda in the warm water and beat into the risen batter until smooth. Cover and leave for 10 minutes.
6. While the batter is resting, gently heat a heavy-based frying pan or griddle and oil it lightly. Oil the insides of the crumpet rings using a paper towel, and set them on the griddle.
7. The batter should now be pourable, like thick cream. If it is too thick you won’t get the essential honeycomb of holes, and if too thin it will run out from under the rings. Cook a small spoonful of batter to test it then thin with a little warm water or add more flour if you need to.
8. Pour 3–4 tablespoons of batter into each ring until half full, and cook gently until the crumpets rise up, the tops are covered with small holes and they are almost dry to the touch. This will take 6–8 minutes. Using a spatula, turn them over carefully, still in the rings, and cook for another 2 minutes. Place on a wire rack to cool and remove the rings after about 5 minutes. Wipe the rings clean, lightly oil them again and make another batch.
9. Toast the crumpets, spread them generously with butter and serve hot with jam or honey or golden syrup. They will keep for a week in the fridge untoasted.