Roasted Carrot Ginger Soup

This is such a comforting soup. I like to finely dice the gingerroot so that I get small bursts of ginger while I'm eating my soup. It is definitely warming and good for cold and rainy or wintery weather. Can be made with Olive Oil instead of butter.

1 lb carrots, peeled and cut into 3" lengths
1 Tbsp mild vegetable oil
1 Tbsp (½ oz/14gr) butter
½ medium onion, diced (to yield about ¾ cup)
1 large rib celery, diced (to yield about ½ cup)
½ inch piece of fresh ginger, minced
2 cups chicken (or veg for Vegetarian) broth
1 tsp salt
⅛ tsp ground pepper
2 cups of water
Chopped fresh chives or chervil for garnish (optional)

1. Heat the oven to 375°F.
2. Chop carrots into 1 to 2" pieces. Drizzle with the oil and place them on a baking dish in a single layer. Roast them in the oven until they start to blister and brown, about 30 to 40 minutes. Browning is essential for flavour.
3. Meantime, in a soup pot, cook the onion in butter until it's soft, about 2 to 3 minutes. 
4. Stir in the celery and ginger and cook until the onions start to brown, about 5 minutes. 
5. Add the roasted carrots, broth, salt, pepper, and and extra 2 cups of water (or if you want a thicker soup, less water). Bring to a boil, cover, and let vigorously simmer until the carrots are tender, about 30 minutes. 
6. Let the soup cool before putting in the blender - hot liquid makes the air expand in the blender urn and the liquid can explode out of the blender and burn.
7. Purée the soup in batches in the blender (also, don't overfill the blender).
8. To serve, return the soup to the pot and reheat it over a gentle flame. Garnish with the chives or chervil.