PreparationIn a large heavy-based saucepan, heat the olive oil and butter over medium-high heat. When the butter starts to foam, add the onion and cook for 3–4 minutes, or until starting to soften. Add the garlic and thyme and cook for another minute, or until fragrant, then add the asparagus and broccoli.
Pour in the stock and a good pinch each of salt and freshly ground black pepper and leave to simmer for 15 minutes. Remove from the heat, stir through the kale and allow to cool.
Blend and then check for seasoning, adding lemon juice, salt and pepper to taste.
Just before serving, toast the seeds in a dry pan until just golden and fragrant. Serve the soup in warmed bowls, sprinkled with the seeds, roughly chopped herbs and cheese if using.