Get a pan on medium heat, add 1 tablespoon of butter.
Thinly slice your potato, toss in bowl with salt, pepper, onion and garlic powder to taste.
Once pan has heated, evenly spread potatoes in pan.
Once first side has browned, flip potatoes and add milk, continuing to cook until milk has reduced and potatoes have browned.
**If you want creamier potatoes, add 1/2 tbsp butter, 1/2 tbsp flour, mixing until combined, then add 1/2 cup of milk, stirring until thickened, and place potatoes back in pan to coat potatoes.**
Butter the outside of each slice of bread.
Place gruyere cheese on bottom slice, stack potatoes, place green onions, cheddar cheese, and top slice.
Fry in a covered pan until golden brown on each side.