500g T45/T55 flour
40g soft unsalted butter
10g instant yeast
140g whole milk (please don't use skimmed)
140g water (try to use filtered or spring)
30g caster sugar
340g cold unsalted butter
Combine everything except the 340g of cold butter and egg into a worktop mixer fitted with a dough hook, and mix on a low speed until the mixture just comes away from the bowl.
Tip the dough out onto the worksurface and shape into a flat disc. Put this disc of dough onto a plate, cover with clingfilm and leave in the fridge overnight.
The next day, take out your cold butter and put it between two sheets of greasproof paper. Bash it with a rolling pin until it becomes a nice square shape, about 15x15cm. Put it back in the fridge for about 20 minutes.
After that time is up, take the dough out of the fridge and, using as little four as possible, roll it out into a slightly larger square than the butter (19cm square). You should be able to fit your sqare piece of butter diagonally on the dough (with the points of the butter square pointing to the middle of the straight sides of the dough square).
Fold the points of dough over the butter like an envelope and press down with your rolling pin, sealing in the butter.
Now roll out your dough/butter parcel to a rectangle measuring 20x60cm. I've found that you roll better if you roll away from yourself, so flip the dough round 180 degrees every so often and keep the flour on the worktop to the minimum amount you can.
With the 20cm side of the rectangle facing you, book fold the dough. Fold the short side away from you so it comes to a quarter of the way up the dough. Fold it over again. It should be halfway up your long strip of dough. Mirror that process with the other end of the dough. Then fold one half over the other so you have a neat rectangle of dough (it should measure 15x20 cm, roughly). Put this in a lightly dusted plastic bag, or wrap it in clingfilm, and put it in the fridge for a minimum of 30 minutes.
Take your chilled dough out of the fridge and put it on the worktop with the short end facing you. Roll away from yourself, continuing the flip and roll you did earlier until your dough measures 20x60 cm again. DO NOT FIGHT THE DOUGH. If you find it isn't rolling easily, put it back in the fridge for 10 minutes. Take your time and don't get frustrated. This time when you fold it, only fold it into thirds (top third folded down, bottom third folded over that). Chill it in the fridge for 30 minutes.
Repeat that roll and fold into thirds one more time. This time, chill the dough for at least an hour. You can leave it overnight if you like.
Roll your dough out to a rectangle about 20x110cm. Again, do not fight the dough. If it gets hard to roll, put it back in the fridge to rest. It would be a shame to ruin two days work now. Every so often when you roll, give the dough a little flip as it will spring and shrink back a wee bit. Let it relax into the shape you want as you want to get your croissants the same size.
Once you're happy with the length and the feel of the dough, start to measure. I like croissants of about 12.5cm at the bottom, but make them whatever size you want. Measure a notch 12.5cm from the short end of the dough and repeat that measurement all along the top of long side. On the bottom long side of the dough, measure and mark a notch 6.25cm from the short end of the dough, and then 12.5cm along from that, repeating the 12.5cm notch along the bottom of the dough. You should have a series of notches along the top and a series of notches along the bottom which are halfway between the ones at the top. Cut diagonally from one notch to the other, making triangles. Cut another notch into the base of each triangle, about 1cm deep.
Use a scalpel, a pizza wheel or a very very sharp knife to mark and then cut your dough. This will make sure you do not damage your layers.
Take a triangle by the bottom and gently pull the top, so it gets long and thin. Do this GENTLY so as not to damage your precious lamination. Then ease the bottom corners out to the side, pulling them gently so that your triangle of dough now resembles the Eiffel Tower in shape.
Pulling the bottom corners of the tower out so that they almost touch the long sides, roll up your croissant from the bottom to the top, stretching the dough as you go. Repeat for all your croissants and put them on a baking tray to prove.
Brush with egg wash and prove in a temperature not exceeding 24degC for about 1 1/2 to 2 hours. Use your judgement. If they are raised, the lamination is clearly visible and they wobble when you shake the tray, they are ready to go in.
Preheat your oven to 210degC. When your croissants are proved, brush with more egg wash and bake for ten minutes, then lower the temperature to 190degC and bake for a further 10-15 minutes.
Cool on a rack and try and wait for a decent interval before devouring.