Melt the butter in a sauce pan over medium heat. Stir in the leeks and add a pinch of salt and a few twists on the pepper grinder. Stir as the leeks cook until they are soft and translucent. Before the leeks start to caramelize, add the stock and bring to a simmer. Simmer leeks for another 10 min. Add peas and bring to a slow simmer for 5 min.

Remove from heat and let cool for 10-15 min. Pour contents into blender and blend until smooth. Return to sauce pan to reheat if needed before serving. Add salt and pepper to taste.