Preheat oven to 425 degrees F.
Coarsely grind coriander, fennel, and red pepper flakes in an electric coffee/spice grinder or with a mortar and pestle. Stir together spices and 1 teaspoon kosher salt.
Cut potatoes lengthwise into 1-inch thick wedges.
Toss wedges with oil and spices in a large roasting pan and roast in middle of oven 20 minutes. Turn wedges over with a spatula and roast until tender and slightly golden, 15 to 20 minutes more.