Melt the butter in a small pot or saucepan over medium heat.
Add in the onions and celery, and sauté until beginning to soften.
Stir in the garlic, and sauté another 30 seconds.
Pour in the milk and vegetable broth.
Add in the potatoes.
Season with thyme, rosemary, salt, and pepper to taste.
Cover the pot, and bring to a light boil, simmering until the potatoes have softened.
Remove from the heat and allow to thicken slightly before serving.
Notes
Use starchy potatoes: Russet or Idaho potatoes work best as they break down and create a creamy texture.Cook the potatoes until tender: Boil them in chicken or vegetable broth until they are soft enough to mash with a fork.Add creaminess: You can add cream, half-and-half, or coconut milk to create a creamy texture. You can also use a hand-held immersion blender to puree some of the potatoes, which will help thicken the soup.Flavorings: Add diced onions, garlic, and herbs such as thyme, rosemary or parsley. To add flavor, you can also add other ingredients, such as bacon, cheese, or chives.Don't overcook: Overcooking can cause the potatoes to become too mushy and break down, resulting in a thinner, less creamy soup.Season well: Taste the soup before serving and season with salt, pepper, and any other spices as needed.