Preheat the oven to 400ºF. Line two baking sheets with parchment paper. Toss the potatoes with 1 tablespoon olive oil and a generous pinch of salt and pepper. Spread the potatoes onto the baking sheets. Roast for 25-35 minutes, stirring once halfway through, until tender and brown in spots.
Meanwhile, prepare the dressing. Heat the remaining 1 tablespoon oil in a small pot over medium heat. Add the shallot. Cook, stirring occasionally, for 2 minutes. Add the garlic and rosemary and stir for 1 minute. Add the broth, vinegar, mustard, and maple syrup. Whisk to combine. Bring to a boil, then reduce heat to low and simmer until the dressing has reduced, about 10 minutes. Whisk in the butter.
In a large bowl, combine the potatoes with the dressing, celery, parsley, and cranberries. Stir to combine. Season to taste with salt and pepper. Serve warm.