Par-roast the sweet potatoes at 400 F until the skin slightly blisters but the center of the sweet potato is still a little undercooked. Let cool, peel and slice into 1-1/4 inch thick discs. Preheat a large pan and add a thin layer of plain olive oil. When hot, sear the sweet potato discs on one side. Flip, add a few knobs of unsalted butter to the pan, and continue to sear the other side. When done, transfer to a hotel pan and season with fine sea salt and fresh black pepper. Wipe the hot pan that you used to cook the sweet potatoes clean, and add 1 quart of veal stock and 1 cup of maple syrup. Reduce to a syrupy glaze (further than you think is necessary). When ready, brush the glaze on top of the sweet potatoes and pour the remaining amount in the pan. For service, rewarm in the oven. When hot, cut each disc into quarters and serve. Before rewarming, you may top with marshmallows if desired.