Peel and dice the potatoes. Add the potatoes to a large pot of boiling water and boil until fork tender, about 8-10 minutes. Drain and set aside.
Cook bacon:
Cook the diced bacon in a skillet over medium heat until cooked through. Move to a paper towel-lined plate to cool and absorb excess grease.
Make potato mixture:
Add the potatoes, sliced butter, sour cream, cream cheese, green onions (reserve some for garnish), bacon (reserve some for garnish), 1 cup of cheese, milk, salt, pepper, and thyme to a large bowl and mix well with a potato masher or hand mixer.
Taste and add more milk if too dry, and more salt and pepper as needed.
Bake potatoes:
Grease a 9×13 baking dish. Pour the potato filling mixture in and bake for 20-25 minutes or until the cheese is melty.
Broil for the last 1-2 minutes. Top with the reserved green onions and bacon. Enjoy!