4 cups (500 g) peeled, halved, cored and thinly sliced Spartan apples
With the rack in the middle position, preheat the oven to 350°F (180°C). Butter a square 8-inch (20 cm) baking dish and line with parchment paper, letting it hang over two sides.
In a bowl, cream the butter and brown sugar. Stir in the flour until crumbly. Set aside 1/2 cup of the dough for the filling. Press the remaining dough into the bottom of the baking dish. Bake for 10 minutes.
Meanwhile, in a bowl, crumble the oats and butter with the reserved dough.
In a large bowl, combine the brown sugar, cornstarch and cinnamon. Add the apple slices and toss to coat well. Spread over the crust and sprinkle with the oat mixture.
Bake for 45 minutes or until the top is golden brown. Let cool on a wire rack before unmoulding.