Meanwhile, prepare the broccoli rabe by rinsing it and spinning it dry in a salad spinner or patting it dry. Slice off the tough lower ends and any stems that are greater than ¼-inch in diameter and discard those pieces. Roughly chop the remaining broccoli rabe into 2- to 3-inch pieces.
Preheat oven to 425 degrees Fahrenheit with racks in the middle of the oven and upper third of the oven. Slice the potatoes into ¾-inch pieces. On a large, rimmed baking sheet, toss the potatoes with 2 tablespoons olive oil and a sprinkle of salt and pepper. Bake for 30 minutes, turning halfway.