Sauté aromatics: Heat a Dutch oven or large pot over medium heat. Add in 2 tablespoons vegan butter, along with the diced onions, celery, carrots, and garlic. Sauté for 4-6 minutes, until onions are translucent.
Form the roux: Add in the remaining 2 tablespoons vegan butter. Sprinkle the all-purpose flour over the vegetables and stir to coat. Cook for about 1-2 minutes, stirring continuously, to cook out the raw flavor of the flour.
Build the soup: Pour in the veggie broth slowly, whisking the whole time to break up any clumps of roux. Then add in the cubed potatoes, bay leaf, and nutritional yeast. Bring the mixture up to a boil, then reduce to medium-low to establish a rapid simmer. Simmer 15-20 minutes, until potatoes are very tender.
Add milk: Stir in the cashew milk (or plant milk of choice) along with the lemon juice.
Mash and/or blend the soup to thicken: Remove the bay leaf from the soup. Use a potato masher to roughly mash some of the potatoes in the pot to thicken the soup. Alternatively, you can use an immersion blender to partially blend the soup — pulse just a few times.
Adjust: Give the soup a taste and adjust salt, pepper, and lemon juice to preference.
Add toppings and serve: To serve, add vegan bacon bits and any of your favorite baked potato toppings, such as vegan cheddar shreds, chopped chives (or scallions), and nondairy sour cream.