Add the Russet Potato (1.5 pound) into a large heatproof bowl and cover with heatproof wrap. Microwave for at least 5 minutes on heat function P10 (or at 1000W) or until the potatoes are soft.
Mash the potatoes with a potato masher/ricer or a fork.
Whisk in the Milk (1/4 cup) and Butter (1/3 cup) until smooth. Season with Salt (to taste) and Ground Black Pepper (to taste).
Add the Onion (1) and Garlic (2 clove) into a skillet with Olive Oil (2 tablespoon) and cook on medium heat for 5 minutes.
Add Ground Beef (1 pound) into the skillet and brown on medium-high heat for 5 minutes.
Defrost the Frozen Mixed Vegetables (1 1/2 cup) for 2 minutes on Turbo Defrost function, 0.5 lb setting.
Add the vegetables, Fresh Parsley (1 bunch), Salt (to taste), and Ground Black Pepper (to taste) into the skillet and cook for another 2 minutes.
Fill each mug 3/4 of the way with the cooked pie filling and use an ice cream scoop to fill 1/4 of the mug with potato mash.
Microwave using heat function for 2 minutes on P10 (or at 1000W) to warm through.
Serve with a small piece of butter and sprinkle with Fresh Parsley (to taste). Cooking results may vary depending on microwave oven use.