Leek & potato soup

Name: Leek & potato soup
Prep time: 10 min
Cook time: 30 min
Total time: 40 min
Yield: 2 servings
Cuisine: European
Ingredients: 1 pinch of Black pepper; 50 ml of Double cream; 1 pinch of Fine sea salt; 1 Leek; 250 gr of Maris piper potato; 1 slice of Unsalted butter; 1 Vegetable stock cube; ½ White onion