Measure the semolina and the flour into a bowl and make a well in it.
Add the yeast to the well and then pour over 100 g of the water. Flick some flour over the top to close the well and let it rest for 15 minutes.
Add the rest of the water and the salt and beat well for 2 minutes or so until there are no lumps and the batter is creamy.
Cover and let sit for 2 hours on a warm day and 4 hours on a cool day. You want the batter to be very airy - full of holes (see picture).
Sieve in the baking powder and mix it in thorougly with a wire whisk to keep as much air in as you can (it can ball up so don't be shy in the mixing).
Let it sit for 15 minutes.
Heat a fying pan slowly on medium - low heat. If you put a pat of butter in the pan on the end of a knife, it should immediatly sizzle. Be patient, don't turn up the heat. You cannot fry a crumpet successfully on high heat.
Grease crumpet rings and place them in the pan so they can get hot too.
Spoon one big spoon of batter in each ring. No more than 1/2 cm of batter in each ring. You may need to push it around with your spoon so the batter completely fills the rings.
Once the rings are all filled, put the timer on for 8 minutes. As you watch, the batter will begin to bubble. After about 6 minutes the holes should begin to appear on the tops of the crumpets at the same time as they begin to dry out. If the holes are closing up again (and you are super keen for holes) open them up with a skewer as they appear (I am being completely serious).
At the end of the cooking time, you should be able to lift the rings away from the crumpets and then remove the crumpets from the pan and place them on a cooling rack. The rings are hot, so be careful. I find a rubber washing up gloves as they are just enough protection and they allow for sufficient dexterity too! You may need to run a little knife around the inside edge of the rings to get the crumpets out.
If you want to flip your crumpets over so they brown on the tops, only do this only once the crumpets are completely dry or you will close up all the holes.
If you want to eat them straight away, cook them for longer so they are completely cooked and crispy on the outside. If you are going to save them for later, only cook them until they are *just* dry because you will toast them before eating them.
They freeze beautifully.