I use a large deep bowl for these potatoes. I use whole milk, no butter. Cover with plastic wrap loosely and/or poke holes in plastic. Keep zapping them and let sit 10 or so minutes each time. Careful when you pull off plastic to not steam-burn yourself. Run a long knife down through the center to keep checking when it gets good and done.
You can use your microwave instead of the oven. It might sound weird to you, but meatloaf does cook well in the microwave. I sauté the onion & green bell pepper, let cool then mix into meat mixture. I use a round glass pie dish and place the meatloaf in a round ring with a hole area in center, cover lightly with good plastic wrap. You have to experiment a little bit with your microwave to get it cooked just right. Take off plastic covering when placing a lot of ketchup on top to finish cooking.