Halve, peel and finely chop the onion. Peel or scrub the carrot. Finely dice it. Finely dice the celery stick. Peel and dice the potatoes. Peel and finely chop the garlic.
Warm a large pan over a medium heat for 2 mins. Add 1/2 tbsp oil. Swirl in your veg with a pinch of salt and pepper. Lower the heat. Sweat for 10 mins till the veg soften.
Stir the mustard into the veg. Add 700ml boiling water and crumble in the stock cube. Bring to the boil. Lower the heat. Simmer for 10 mins or till the veg are tender.
While the soup simmers, tip the pumpkin seeds into a dry frying pan. Toast over a meidum hat for 2-3 mins till they smell nutty and are a little browned. Tip into a bowl and set aside.
Finely shred half the wild garlic leaves and add to the soup (see our tip below). Ladle into a blender and whizz to make a smooth soup, or use a hand-held blender in the pan. Taste and adjust the seasoning. Ladle the soup into warm bowls and scatter over the toasted pumpkin seeds to serve.