Place the non-dairy milk, corn, nutritional yeast, salt, garlic powder, and black pepper in your blender. Stir with a spoon and set aside for now.
Place the cauliflower florets, diced potato, and water in the inner pot of your Instant Pot (IP) and lock the lid into place, making sure the nozzle is pointed in the sealing position. Set the timer for 3 minutes on Manual (or Pressure Cooking) mode. When the timer goes off, use the natural release method for 5 minutes and then manually release the remaining pressure. Drain the veggies, discard any remaining liquid, then transfer to a large mixing bowl. Set aside for now.
Blend the corn mixture that’s in your blender until it’s creamy and smooth. Transfer the blended mixture to a small saucepan and simmer for 5 minutes, over medium-low heat, stirring frequently so it doesn’t burn. Pour the mixture over the potatoes and cauliflower and mash with a potato masher or large fork until the veggies are well mashed and the corn mixture is thoroughly combined.
Add salt and pepper to taste and store in the fridge when completely cooled.