Preheat the oven to 190°C /Gas 6.
Place the sweet potatoes on a baking tray and roast them in the oven for about 45 minutes to an hour or until they are soft in the middle when pierced with a knife. The cooking time will depend on the size of the potatoes. For larger potatoes, you may need to leave in the oven for a bit longer.
Coat the parsnip pieces in the olive oil and lay them on another baking tray. Roast in the oven for about 30 minutes, or until the parsnips are soft in the middle when pierced with a knife.
Meanwhile, heat a deep saucepan over a medium heat and fry the lardons until brown. You will not need to add any oil before frying as there is enough fat in the lardons. Remove the saucepan from the heat to prevent the bacon burning while you prepare your other ingredients.
Once the parsnips are cooked, add these to the saucepan. Scoop out the cooked flesh of the potatoes and add this to the saucepan along with a little of the chicken stock. Return the saucepan to a low heat and, using a hand blender, begin to blend all the ingredients together, continuing to add the chicken stock gradually until you have a smooth consistency.
Add all the remaining stock, mix together thoroughly and season well with salt and pepper. Cook on the hob for about 10 minutes over a low to medium heat to allow all the flavours to infuse.
Serve with an indulgent drizzle of cream if desired and some crusty seed bread.
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Freezing and defrosting guidelines
Make the soup, then leave to cool at room temperature. Freeze (without garnishes or toppings) in a rigid container, leaving a bit of space for expansion, for up to 1-3 months. Reheat either from frozen or defrost in the fridge overnight. Once piping hot, add toppings or garnishes and serve.
For top tips on protecting you and your family when preparing raw meat and poultry, visit Food Safety in the Home and view the full Food safety at home video.