1. Preheat oven to 200°C. Peel and dice the sweet potatoes, place on a baking tray and drizzle with 1 tablespoon of oil. Season with 1/4 tsp salt and 1/4 tsp pepper. Bake for 30 minutes until golden brown, turn occasionally. Allow to cool.
2. Heat 1 tablespoon of oil in a pan, fry the corn over high heat for 5-10 minutes, then let cool. Cut the radicchio into quarters lengthwise and sauté in the same pan over medium heat. Separate the corn grains with a knife and cut the radicchio coarsely.
3. Cut dill and chives into small pieces and mix with buttermilk, yoghurt, mayonnaise, lemon juice, mustard, honey, garlic, remaining salt, pepper and olive oil in a bowl.
4. Pluck Romaine lettuce. Cut the onion into thin slices and mix with the salad and 2 tablespoons of the dressing and serve. Cut the bacon, chicken, avocado and courgette into small pieces. Cut tomatoes and eggs in half. Add everything together with sweet potatoes, corn, radicchio and cheese to the salad. Serve the rest of the dressing separately.