01 - Melt butter in a large pot over medium heat. Add leeks and onion, sauté for 6-8 minutes until softened and translucent, stirring occasionally to prevent browning.
02 - Stir in minced garlic and cook for 1 minute until fragrant, being careful not to burn.
03 - Add diced potatoes, salt, pepper, and bay leaf to the pot. Pour in vegetable stock, ensuring all vegetables are completely submerged.
04 - Bring mixture to a boil, then reduce heat to low and simmer uncovered for 20 minutes or until potatoes are fork-tender and easily crushed.
05 - Discard the bay leaf from the soup.
06 - For chunky texture, lightly mash some potatoes with a spoon. For smooth consistency, puree with immersion blender or in batches using a regular blender until silky.
07 - Stir in milk and gently heat for 2-3 minutes without boiling. Adjust salt and pepper seasoning to personal preference.
08 - Ladle soup into bowls and garnish generously with chopped fresh parsley.