Brown the rack of lamb on all sides in a very hot frying pan. Remove from the heat and immediately brush with Dijon mustard.
Combine the cheese, sage, breadcrumbs and a little oil. Roll the lamb in the breading. Roast the lamb in the oven at 180°C for about 15-18 minutes, depending on size. If you’re using a meat thermometer, it should have a core temperature of around 58-60°C. When you press on the meat, it should feel firm. The cooking time may vary depending on the size of the rack.
Let it stand for approx. 5-7 minutes before carving.
Cook the lentils with the bay leaf, garlic, salt and pepper until tender. It should take about 20 minutes. Drain off any excess liquid.
Sauté the finely chopped shallots, garlic and bay leaves in a little oil. Add the red wine and reduce by about half. Now add the stock and again reduce by about half. Strain out the shallots, then whisk butter into the sauce. Season to taste with salt and pepper.
Cut the radicchio head into slices that are held together by the stem. Sear them on both sides in a little olive oil. Add the stock and sage leaves, cover and braise for about 5 minutes over medium heat.
Sprinkle with a little grated Castello Tickler Mature Cheddar cheese just before serving.
Assemble the dish with the lentils in the bottom. Then add the radicchio with cheese and the lamb. And top with a little sauce.