1. Peel and dice the potatoes, carrots and onions.
2. Melt the olive oil and butter in a saucepan.
3. Add the chopped vegetables and sauté for about 5 minutes.
4. Add the mustard, flour and vegetable stock.
5. Cook until the vegetables are soft.
6. Then blend the soup until smooth.
7. Season with salt and pepper.
8. Serve warm.