Gently warm the milk, then pour into a large bowl with 100ml of tepid water. Stir in the yeast and sugar to dissolve. Leave in a warm place for 15 minutes, or until frothy.
Sift the flour, bicarbonate of soda and 1 teaspoon of fine sea salt into a large bowl. Make a well in the centre and pour in the yeast mixture.
Whisk from the centre outwards until the consistency of double cream – this will take a few minutes. Add a splash more water, if needed.
Cover with a damp tea towel and set aside for 45 minutes, or until little bubbles form on the surface.
Wipe a little oil around a 24cm non-stick frying pan and place over a medium heat.
Once hot, pour half of the batter into the pan, and cook for 6 minutes until little bubbles appear on the surface. Once the bubbles have burst, carefully flip the crumpet over to cook for a further 4 minutes until it’s begun to brown on the other side.
Transfer to a board and repeat with the remaining batter. Cut the giant crumpets into quarters and serve with your favourite toppings.