Preheat oven to 425°F. Line a large baking sheet with parchment paper or lightly oil it.
Wash and halve potatoes to roughly 1½ inch pieces for even cooking. Pat completely dry with a paper towel—dryness is crucial for crispiness.
In a large bowl, combine potatoes with olive oil, kosher salt, black pepper, garlic powder, and smoked paprika. Toss until every piece is coated evenly.
Arrange potatoes in a single layer on the baking sheet with cut-side down. Do not overcrowd—they need space to crisp, not steam.
Roast for 20-25 minutes without stirring. The cut sides will turn golden and crispy.
Flip potatoes and roast for another 15-20 minutes until deep golden and crispy on all sides.
Remove from oven. Scatter fresh thyme over hot potatoes if using. Finish with a pinch of fleur de sel.
Transfer to serving bowl and serve immediately while still crispy and warm.