Place flank steak in a large ziplock plastic freezer bag. Stir together garlic, rosemary, thyme, crushed red pepper, 1 teaspoon of the salt, and 1/2 teaspoon of the black pepper in a small bowl. Whisk in 1/4 cup of the olive oil, and pour over steak. Seal bag, and turn to coat. Chill 30 minutes or up to 24 hours.

Place top oven rack 6 inches from heat. Preheat oven to 450°F. Stir together potatoes, butter, and remaining 1 tablespoon oil, 1 teaspoon salt, and 1/2 teaspoon black pepper. Spread in an even layer on a heavy-duty aluminum foil-lined rimmed baking sheet.

Bake potatoes in preheated oven 20 minutes. Remove from oven, and move potatoes to outer edges of pan. Place kale in center of pan, and top with steak. Increase oven temperature to broil.

Broil 6 minutes. Turn steak, stir vegetables, and broil 6 minutes more or to desired degree of doneness. Remove from oven, and let stand 5 minutes. Cut steak across the grain, and drizzle with pan drippings. Serve steak with kale and potatoes.