Warm the olive oil and butter in a large pot over medium heat. Add the onion and sauté for 5 minutes. on low heat, add your garlic and celery, and cook for an additional 5 minutes until your celery is slightly softened . Sprinkle in all of your seasonings and let them bloom in the fat for 30 seconds to one minute until fragrant
Add the potatoes and stir to coat with the aromatics and spices. Pour in the vegetable broth and bring to a gentle simmer. Once simmering, cook the potatoes for 18 minutes, or until tender and easily breaking apart when pressed with a fork
Mash about half of the potatoes, then keep the rest as whole pieces so the soup has a mix of textures
Lower the heat to medium-low and pour in the milk and cream. Let the soup gently simmer (not boil) for 5–7 minutes to warm the dairy.
Stir in the sour cream, cheddar, and parm slowly on low heat, until everything melts and becomes smooth. add in your corn starch slurry, Taste and adjust with fine sea salt (or any of your other seasonings) , letting it sit on low heat until you hit the consistency you prefer
To make the crispy shallots, heat avocado oil in a small pan over low-medium heat. Fry the sliced shallots for 5–7 minutes until golden brown and crisp. Transfer to paper towels to drain
Ladle the soup into bowls and top with the crispy shallots, a dollop of sour cream, freshly grated cheddar, fresh chives or green onion
and you're done!