Tip the flour into a mixing bowl and add the yeast and sugar on one side and the salt on the other side. Mix well then stir in the milk and stock until you get a smooth batter. Leave to rest in the fridge for 2 days.
Trim as much meat from the fat as possible and freeze the fat for an hour. Chop into small chunks (or blitz in a food processor but make sure it’s almost frozen). Add the fat to a medium saucepan and put it over a low heat. Warm the fat for a few hours to render, then strain through a fine sieve. Seal in a jar and store in the fridge.
To make the crumpets, place a 5cm metal ring in a non- stick pan with the lamb fat. On a very low heat add enough crumpet batter to be 2cm deep and let it cook through. Holes should appear on the top of the crumpet. Once it has cooked through, take it out of the ring and set aside. They can then be kept for up to 5 days before toasting or baking.
Put the Dijon mustard, egg yolks, garlic, cocoa powder and charcoal powder into a mini food processor then blitz. Slowly drizzle in the oil as it’s blitzed, until the mixture thickens enough to hold it’s shape. Squeeze in a little lemon juice to taste. Season with salt and pepper, push through a sieve and set aside until needed.
Preheat the oven to 180°C. Season the lamb with salt and pepper then rub the mayo all over. Put a frying pan over a high heat until smoking hot. Turn the heat down to medium and add the lamb. Cook on each side until it’s a deep golden brown. Put the lamb in the oven for 10-15 minutes, so the core temperature is 55-60°C (for medium). Let the lamb rest for 10 minutes.
Put a griddle pan over a high heat and preheat for a few minutes. Cut the lettuce in half lengthwise and press them into the pan cut side down. Cook for 3-4 minutes, until the cut side blackens in places.
Whisk together the vinegar, olive oil and mustard in a mixing bowl. Lightly toss each lettuce half in the dressing, seasoning with salt and pepper.
Preheat the grill to high, generously brush the crumpets with more lamb fat and grill until golden brown on top. Plate one lettuce half per plate with 2 crumpets and 2-3 lamb cutlets. Place a dollop of the mayo onto the plates and serve.