In the same bowl, mix together rolled oats, butter, sugar and flour.
1 cup (85g) rolled oats, 3/4 cup (170g) unsalted butter, 3/4 cup (150g) granulated sugar, 1/2 cup (65g) all-purpose flour
Mix in walnuts, baking powder, nutmeg and salt. Spoon the batter evenly over the apple mixture.
1/2 cup (60g) chopped walnuts, 1/2 tsp baking powder, 1/4 tsp nutmeg, 1/4 tsp salt
Bake for 45 - 60 minutes or until the filling is bubbling and the top is golden brown.
Notes
Serve warm, room temperature, or cold with a dollop of whipped cream, warm vanilla cream sauce, or a scoop of vanilla or cinnamon ice cream.Leftovers can be tightly cover with saran wrap or transfer to an airtight container and store at room temperature for up to 2 days or in the fridge for up to 5 days.To make in advance - Prepare the whole pie, cover, and refrigerate up to one day in advance. When ready to bake, bring the pie to room temperature by placing it on the counter for 1 hour, then bake as instructed.