Melt butter in a large pan and add onions, carrot, and celery.
Tear in rosemary and bay leaves and cook for a few minutes before adding garlic.
Add lentils and 1 litre of vegetable stock to the pan.
Bring to the boil and then simmer while preparing the pumpkin.
Add 600g of pumpkin chunks to the stew and season with salt and pepper.
Pour over enough water to cover ingredients, cover with a lid, and simmer for 30–40 minutes.
Stir in the chopped parsley when the stew is almost ready.
Remove one bowlful of stew and blend it with 200ml of stock until smooth.
Return the blended mixture to the pan for a velvet texture.
Serve in bowls and top each portion with a spoonful of sour cream.