Celeriac and Ginger soup

Ingredients

• 2 lb celeriac (, peeled and cubed)
• 1/2 cup of ginger (, peeled and sliced)
• 1 large carrot (, peeled and diced)
• 1 large onion (, cubed)
• 3 sprigs of fresh thyme or 1/2 teaspoon of dry leaves
• 3 tablespoons of olive oil
• 6 cups of vegetable stock or 2 vegetable bouillon cubes dissolved in 6 cups of water
• Salt
• Pepper