Mix flours, yeast, salt, and 255ml of water in a bowl to form a dough.
Knead for 10 minutes and leave in an oiled bowl to double in size for 3 hours.
Shape dough into a flat rectangle on an oiled surface and make dimples with your fingers.
Transfer to a lined tray and prick the middle with a fork, leaving the rim untouched.
Leave dough in a warm place to prove for 60 minutes.
Bake in a preheated oven at 220°C for 30 minutes until golden-brown.
Marinate lamb steaks in rosemary, garlic, lemon zest, and oil for at least 30 minutes.
Mix crème fraîche, lemon juice, and mustard in a bowl to create the dressing.
Sear lamb in a hot griddle pan for 3 minutes per side and let rest.
Place trencher on a board and top with watercress, beans, spring onions, and radishes.
Slice the lamb on a slant, arrange over the salad, and top with dressing.