Pumpkin soup

1 medium onion, peeled and roughly chopped

750g butternut squash or pumpkin of your choice, peeled and cut into cubes 

1 carrot, peeled and roughly chopped 

1 stick celery, roughly chopped 

3 garlic cloves, crushed 

2 tbsp olive oil 

1 tsp ground ginger 

700 ml chicken or vegetable stock