Preheat the oven to 400°F.
To make the relish, toss the cauliflower florets with olive oil, salt and pepper on a baking sheet and roast for 12-15 minutes, until browned and fork-tender. Chop the roasted cauliflower into small pieces and transfer to a bowl.
Add the currants, dill and pickled red peppers to the cauliflower and toss to combine.
For the soup, melt the butter in a large saucepan. Add the onion and garlic and cook on low heat until softened but not colored, about 5 minutes.
Add the cauliflower and cook until softened, about 10 minutes.
Stir in the wine, cream, broth, and salt to taste. Bring to a simmer and cook until the cauliflower is fork-tender.
Add the sour cream and lemon juice and purée the soup with an immersion blender or in a regular blender (let it cool a bit first to avoid splashing). Adjust seasoning with salt and pepper.
To serve, divide the soup between bowls and garnish with cauliflower relish.