Heat butter and 1 tbsp oil in a saucepan over medium heat, add onion and garlic and stir occasionally until onion softens and starts to caramelise (10 minutes). Add apple, potato and parsnip and stir to combine, then add stock and oregano, season to taste and bring to the boil. Reduce heat to medium and simmer until potato and parsnip are tender (15-20 minutes). Blend with a hand-held blender, then add cream, stir to combine and season to taste.
Preheat oven to 180C. Place baguette slices on an oven tray, brush with butter and bake, turning once, until golden (5-8 minutes).
Meanwhile, separate the Brussels sprouts leaves, quarter the hearts and stand in a bowl of cold water to crisp (5 minutes). Drain well, and pat dry with a tea towel. Heat remaining oil in a frying pan, add sprout hearts and fry, turning occasionally, until golden (2-3 minutes), then set aside on a plate and keep warm. Add Brussels sprout leaves to pan and fry until just starting to soften (30 seconds-1 minute).
Ladle soup into bowls, scatter with baguette croûtons, Brussels sprouts and parmesan, drizzle with extra oil and serve hot.
Note This recipe makes 1.5 litres of soup.
This recipe is from the May 2013 issue of Australian Gourmet Traveller.