Trim leeks, leaving some green for colour in the soup.
Slice leeks into 5mm pieces after cutting them in half lengthwise.
Rinse leeks in a colander with cold water and drain.
Peel and slice the onion to match the leek thickness.
Heat a pan over medium heat, melt and foam butter.
Add chopped leeks and onions, and coat in butter. Stir occasionally for 10 minutes under a cover.
Slice potatoes into 5mm pieces after peeling.
Add potatoes to the pan, and pour in the hot stock. Season lightly.
Add nutmeg, bring to a boil, then simmer covered for 10 minutes.
Blend with an electric hand blender after removing from heat.
Heat Mary Berry Leek and Potato Soup to boiling.
Remove from heat, add cream and lemon juice. Stir and garnish with parsley.