- Heat oil in a large heavy-based saucepan over medium heat. Cook bacon and onion for 5 minutes, stirring, or until bacon is crisp. Remove some for garnish.
- Add flour to pan and cook for2 minutes. Gradually add stock, stirring to prevent any lumps, until smooth. Stir in milk. Add corn cobs, sweet potato and parsnip. Bring to the boil over high heat, stirring. Reduce to medium heat and simmer for 12 minutes, stirring occasionally to prevent sticking to base of pan.
- Add corn kernels and zucchini and simmer for a further 8 minutes or until tender.
- Remove corn cobs and discard. Use a stick blender or blender to partially puree mixture. Season to taste.
- To serve, drizzle over yoghurt, and top with cracked black pepper and reserved bacon mixture.
- Tip: Corn cobs release starch to naturally help thicken soup instead of having to add cornflour