If you are a fan of nuts, this oatmeal pairs quite well with almonds. You may stir a quarter to a half cup of toasted, slivered almonds into the batter if you like the added flavor and crunch. Or, simply sprinkle some nuts over the top prior to baking. Pecans and walnuts compliment this dish well, too.
The mascarpone adds an extra layer of flavor, but this dish is delicious without, too.
Grease a 12-inch cast iron skillet or 9×13 baking dish.
In a large mixing bowl, combine all ingredients except the oats, mascarpone, and brown sugar. Stir in the oats and combine well. Transfer the mixture to the prepared skillet and spread evenly around. Dot the mascarpone cheese evenly across the top, and then cover tightly with plastic wrap or foil and refrigerate overnight.
In the morning, preheat the oven to 375 degrees. Allow the oatmeal to sit on the counter while the oven is preheating. Uncover the oatmeal and bake for about 35 minutes or until just firm in the middle.
Remove from the oven, switch oven setting to broil, and sprinkle brown sugar over the top. Broil oatmeal for one minute, watching closely, or until the sugar is melted and top is golden.
Notes
I have made this recipe oodles of different ways, including with the grated apple or the applesauce, both, and neither. Including the applesauce along with the juicy peaches provides more moisture and a hint of a custard flavor, thanks to the four eggs. Omitting the apple and/or applesauce yields a slightly less moist finished product, yet not at all dry. In my mind, both versions are equally delicious yet slightly unique.