Preheat the oven to 180°C/350ºF/gas 4. Peel and finely slice the garlic, then place it in a large casserole pan on a medium-high heat with 2 tablespoons of olive oil and the frozen mixed veg. Fry for a few minutes while you slice 500g of the mushrooms, then add them to the pan with a good pinch of black pepper. Cook for 10 minutes, or until golden, then pour in the stock and cook for a further 10 minutes. Meanwhile, slice the remaining 250g of mushrooms (slice them so you have some beautiful cross- sections, throwing any trimmings into the soup as you go), place on a tray with a drizzle of olive oil and a pinch of sea salt and pepper, and roast for 15 minutes, or until beautifully golden and crisp.
When the time’s up, blitz the soup to your desired consistency, then season to perfection. Divide between warm soup bowls, ripple 1 tablespoon of sour cream into each, and top with the crispy mushrooms and a little drizzle of extra virgin olive oil, if you like.