Heat oil over a medium heat in your Biroix dish add your onions and whites of the leek. Cook for 3 minutes, add the carrot and butter cook, stirring occasionally, for around 2 minutes. Then add the greens of the leek, and the garlic, season well, cook until all vegetables look lovely and sauteed, around 5 minutes.
To make it vegetarian use vegetable stock
Herbs – this recipe is really adaptable, I love using coriander, sage is also lovely. If using more woody herbs like rosemary or thyme, add them when you add the potatoes.