In a large bowl, toss the potatoes with the olive oil, rosemary, fennel seeds, red pepper flakes, 1/2 tsp. salt, and a few generous grinds of pepper. Arrange them cut side down in a well-spaced single layer on a rimmed baking sheet or in a shallow roasting pan, making sure to scrape out and include any herbs and oil stuck to the bowl. Roast for 20 minutes and then stir the potatoes with a spatula and scatter the garlic cloves over them.