Place the potatoes and garlic in a large saucepan. Cover with cold water by about 1 inch, stir in 1 teaspoon kosher salt, and bring the water to a boil.

Reduce the heat to a steady simmer and cook for 18–25 minutes. The potatoes are ready when a fork slides through the centers without resistance.

Drain the potatoes and garlic thoroughly, then return them to the warm pan for 1–2 minutes. This allows excess moisture to evaporate and keeps the finished mash from becoming watery.

Mash the hot potatoes and garlic, then add 4 tablespoons butter, the warm cream or milk, Parmesan if using, black pepper, and additional salt to taste. Mash just until creamy and smooth, taking care not to overwork the potatoes.

Transfer the mashed potatoes to a buttered 2-quart baking dish or ovenproof skillet. Spread the surface into an even layer so the panko topping can brown consistently.

Combine the panko with the remaining 1 tablespoon melted butter or olive oil. For especially even color, toast the panko briefly in the fat for about 5 minutes before scattering it over the potatoes.

Bake at 400°F (200°C) for about 8–10 minutes, until the topping is golden and crisp. Alternatively, broil for 1–3 minutes, watching closely because panko can darken quickly.

Garnish with chopped parsley or chives and serve hot. Spoon through the crunchy crust so every portion includes both the crisp topping and creamy garlic potatoes.