Heat oil in a 12-inch cast-iron skillet over high heat.
Add fennel and cook, stirring often, until it starts to brown, 4 to 5 minutes. Season with fennel seed, salt and pepper.
Add tomatoes, bring to a simmer and cook until the tomato juices are slightly reduced, about 4 minutes. Add potatoes and ½ cup broth (or water); cover the pan tightly and simmer over medium-low heat, checking every 10 minutes to make sure the pan juices don’t run dry.
If necessary, add more broth (or water), 2 tablespoons at a time, to prevent scorching. Simmer until the potatoes are tender, about 20 minutes.
Uncover, add Pernod (or other liqueur), if using, and simmer for 3 to 4 minutes more. Serve garnished with parsley (or fennel fronds), if desired.