Place potatoes in a large pot and cover with cold water by 1 inch. Add 1 tbsp kosher salt. Bring to a boil, then simmer for 15-20 minutes until just fork-tender. Do not overcook.

Drain potatoes in a colander and let them sit for 5 minutes to steam dry.

Preheat oven to 450°F (230°C). Line a baking sheet with parchment paper and drizzle with the 3 tbsp of high-heat oil.

Arrange the boiled potatoes on the baking sheet, spacing them well apart. Using a flat-bottomed glass or cup, gently but firmly smash each potato to about 1/2-inch thickness.

In a small bowl, mix together the 1.5 tbsp olive oil, minced garlic, rosemary, thyme, 1 tsp coarse salt, pepper, and garlic powder (if using).

Brush or spoon the garlic-herb oil mixture generously over the top of each smashed potato.

Roast for 25-35 minutes, or until deeply golden brown and the edges are dark and very crispy.

Remove from oven. Sprinkle immediately with flaky sea salt and fresh parsley. Serve hot.