Peel the potatoes if desired. Then, cut them into quarters.
Add potatoes to a large pot. Fill with cold water, about an inch or two above the potatoes. Bring to a boil and let cook until the potatoes are soft and fork-tender, about 12-16 minutes.
Carefully drain the potatoes into a colander. Then, put the potatoes back into the warm pot.
Mash potatoes with a potato masher.
In a small pot, whisk together the non-dairy milk, garlic, and onion powder. Add in the vegan butter and melt it on medium-low heat. Let it simmer for about 2 minutes, whisking frequently.
Carefully pour the warm butter mixture into the pot with the potatoes. Stir well. If you think the potatoes need more moisture, warm up some more non-dairy milk and add as needed.
Add salt and pepper to taste.
Notes
*Medium potatoes are about 2-3 inches in diameter.