Averie Cooks

0 To a large Dutch oven or soup pot, add 2 tablespoons butter, and heat over medium-high heat to melt.
1 Add the flour to the melted butter, and using a wooden spoon, stir constantly until dissolved.
2 Add the remaining butter, leeks* (see Notes), onions, salt, pepper, and saute for 5 minutes, or until vegetables begin to soften; stir frequently. Tips - I like to use sweet Vidalia onions for their flavor, but yellow or white onions may be used. Adding the salt now helps sweat the vegetables and adds a better flavor to the soup. Because I use reduced sodium broth, I find 2 teaspoons salt now to be necessary, but always salt to taste. 
3 Add the garlic and saute for 1 minute; stir continuously.
4 Add the reduced sodium chicken broth, potatoes, thyme, and bring to a simmer.
5 Reduced the heat to medium or medium-low, cover the Dutch oven, and simmer  for about 20 minutes, or until potatoes are very tender and soft.
6 Remove the sprig of thyme and using an immersion blender, blend the soup to. your desired consistency. Tips - If you don't have an immersion blender, you can blend the soup in a high speed blender. When working with hot liquids in a blender canister, always pay attention that there's a way for steam to escape. For me, the easiest way to achieve this is to pop out the plastic piece in the lid, and cover that hole with an old dish towel. You still need to cover the hole with something so soup doesn't go flying everywhere, but just not sealed off like you would have with the plastic piece still in. Blend in two or three rounds if necessary.
7 Add the milk, stir to combine, taste the soup for seasoning balance, and add additional salt or pepper, if desired, to taste. Tip - If the soup tastes at all flat, boring, or dull, it likely needs more salt. Don't be afraid to add it. I add about 3-4 teaspoons total salt (2 to start and nearly 2 at the end) because you're seasoning and flavoring pounds-worth of very basic root vegetables which need salt to bring out their best so don't be afraid to add salt.
8 Optionally, garnish the soup with fresh chives, parsley, thyme, and serve. Soup will keep airtight in the fridge for up to 5 days or in the freezer for up to 3 months. Reheat very gently as desired in the microwave or on the stovetop.