Toss the chopped apples with the maple syrup and place them in a 2 1/2 quart baker (see notes for alternatives.)
Whisk together the flour, cinnamon, nutmeg, and salt, and maple sugar in a mixing bowl. Add the butter, cut into pieces, and rub together with your fingers until there are no large chunks of butter remaining.
Stir in the walnuts and oats, and sprinkle the crumbly mixture evenly over the apples.
Bake for about 45 minutes until golden brown and the apple juices are bubbling.
Serve warm with vanilla ice cream, if desired.
Leftovers can be stored on the counter for up to 3 days, and in the fridge for up to a week.
Nutritional information is provided as a courtesy and is an estimate only. This information comes from online calculators. Although The View from Great Island attempts to provide accurate nutritional information, these figures are only estimates.
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