Preheat oven to 350 degrees F. Meanwhile, in a medium pot over high heat, cover potatoes with water and bring to a boil. Reduce to a simmer; cook until potatoes are just tender, 10 to 15 minutes. Drain potatoes and let rest until cool enough to handle. Cut each in half lengthwise. Set aside. In a large skillet over medium-high heat, cook bacon until crisp, about 6 minutes per side. Remove skillet from heat and stir in maple syrup and cayenne. Set aside. Butter a 2-quart baking dish and set aside. In a large bowl, stir reserved potatoes and maple-bacon mixture, plus cheese and scallions, to combine. Transfer to prepared baking dish. Set aside. In a large bowl, whisk eggs, milk, salt, and freshly ground pepper to combine. Slowly pour over potato mixture. Bake until top is golden, about 50 minutes.