For the soup:

1. Melt butter in a large Dutch oven or similar heavy bottomed pan over medium heat. Add leeks, thyme and bay leaf. Add a pinch of kosher salt and sauté for about 10 minutes until tender.
2. Stir in potatoes to combine and season with fresh ground pepper. Add stock and bring to a boil, reduce heat to medium-low and cook until potatoes are done, about 15 minutes. Remove from heat and allow to cool.
3. Working in batches, put the soup in a blender, filling it up to no more than 2/3 capacity. Each batch should be comprised of both potatoes and broth. Put the lid on the blender and firmly hold the lid on securely while blending each batch until smooth. 
4. Return all the blended soup to the original pot over low heat and season with miso, lemon juice and lemon pepper. Pour into individual bowls and garnish.

For the garnish:

1. While the soup is cooking, heat a frying pan to medium high. Add a splash of olive oil. When the oil is hot, add the prosciutto slices, cooking them in batches and flipping each strip after a minute or two. Cook until crisp. Remove from the pan and place on a paper towel-lined plate to remove extra oil. Crumble the prosciutto strips.
2. Garnish the soup starting with the feta cheese so it is the first garnish to hit the hot soup, then adding crumbled prosciutto, chives or green onions, a few drops of hot chili oil and a sprinkling of crushed red pepper flakes.