Preheat the oven to 450 degrees F.
Put the potatoes in a large bowl and pour over the olive oil. Add big pinches of salt and pepper. Add the chili powder and garlic and toss together well.
Spread the potatoes in a single layer onto 2 baking sheets. Bake, tossing them halfway through the cooking time, until crispy, about 30 minutes. Remove to a platter, season with additional salt and serve.