Thinly slice the leeks and garlic and finely chop the rosemary. Melt the butter in a skillet over a medium heat and add the leeks, garlic, lemon zest, rosemary, salt and pepper. Stir well to combine and pan fry for 3-4 minutes or until the leeks are tender and cooked through.
Step 2
Stir through the creme fraiche and mustard and remove from the heat. Serve immediately.