Use plain pumpkin puree, never canned pumpkin pie filling, which is already sweetened and spiced.
Old-fashioned rolled oats only. Steel-cut oats stay hard and gritty in the oven, instant oats collapse into mush.
Stir the wet into the dry just until no dry patches remain. Aggressive mixing pulls starch out of the oats and turns the finished dish gummy.
Serve with cold milk or cream poured over each square, the Lancaster County way. Plain or vanilla yogurt, a drizzle of maple syrup, chopped toasted pecans and fresh fruit are all good on the table alongside. Hot coffee is not optional.
Assemble the night before, cover and refrigerate, then bake straight from the fridge adding 5 to 8 minutes to the time.
Keeps 5 days covered in the refrigerator. Reheat squares in a 325 F oven for 10 minutes or microwave 45 seconds.