Place baby potatoes in a large pot, cover with cold salted water, and bring to a boil. Reduce to a steady simmer and cook for 15–20 minutes, until easily pierced with a fork.

Preheat oven to 425°F (220°C). Line a large rimmed baking sheet with parchment paper or lightly grease it.

Drain potatoes thoroughly and allow them to steam-dry for about 5 minutes.

Arrange potatoes on the prepared baking sheet and gently smash each potato to about 1/2 inch thick using a potato masher, sturdy glass, or measuring cup.

Combine olive oil and melted butter. Brush over the potatoes and season evenly with garlic powder, smoked paprika, dried thyme, salt, and black pepper.

Roast for 25–30 minutes without flipping, until the bottoms and craggy edges are deeply golden and crisp.

Meanwhile, cook chopped bacon in a large skillet over medium heat for 5–7 minutes until crisp. Transfer bacon to a paper towel-lined plate, leaving about 1 tablespoon bacon fat in the skillet.

Add mushrooms and sliced onion to the skillet and cook over medium-high heat for 7–9 minutes until the mushrooms are browned and onions are tender.

Add minced garlic, thyme, and black pepper and cook for 30–60 seconds until fragrant. Stir most of the cooked bacon back into the mushroom mixture.

Remove crispy potatoes from the oven and spoon the mushroom, onion, and bacon mixture over and around them. Sprinkle evenly with shredded cheese.

Return to the oven for 4–5 minutes, until the cheese is melted. Broil for about 1 minute if additional browning is desired.

Top with reserved crispy bacon and chopped fresh parsley. Serve immediately while hot and crispy.