Heat 1 tbsp oil in a large saucepan, and add the garlic and rosemary or bay leaf. Stir for a couple of minutes until the aromas are released.
Make sure your kale and mustard leaves (if using) are really finely chopped: this will give a better texture when cooked. Rinse and put in the saucepan without drying, stirring to coat in the garlic and herbs. Add 0.5cm (