Melt the butter and oil in a large saucepan. Add the onions and celery, and gently cook until really soft – about 15 mins.
Add the squash and cook, stirring for 5 mins.
Add the honey and chicken stock, bring to a simmer and cook until the squash is tender.
Remove from heat and using a hand blender, blitz until smooth (adding a bit more stock or water if the soup is too thick). Season to taste with salt and pepper. Reheat before serving, sprinkle with chopped parsley.
For the winter squash - you can buy whole squash and prepare them yourself, or buy bags of ready to use.