Lightly spray a baking pan, preferably an 8 x 12″, although the recipe isn’t particular and almost any size will work from a 9 x 9″ up to a 9 x 13″; the difference will be in thickness and the thicker the baked oatmeal, the longer it will need to cook, so go up or down on timing as needed.

When ready to bake, preheat oven to 350 degrees F.

In a large bowl, whisk together the oats, baking powder, cinnamon, nutmeg, salt, and brown sugar. In a smaller bowl, mix the milk, eggs, and vanilla. Immediately whisk vigorously to combine so the butter doesn’t harden in the cold milk. Pour over the oatmeal mixture and stir together.

Distribute the diced apples (and raisins if using) evenly over the bottom of the baking dish; pour the oatmeal mixture over the top. Cover and refrigerate overnight.

When ready to bake, uncover and bake for 30 to 45 minutes until top is golden brown and apple pieces, when pierced with a fork are tender. The mixture should be set around the outside edges but will be a bit moister in the middle. When pressed it’s ok to be a bit soft but shouldn’t be “sloshy.” It will continue to firm a bit as it cools.

Serve warm or at room temperature, with powdered sugar, milk or cream as desired.