Heat oven to 350°F. Grease a 9-inch pie dish and line the base with parchment.
Whisk the flour, baking soda, and salt for the cookie crust in a bowl.
Cream softened butter with granulated and brown sugar until fluffy. Mix in vanilla, then the beaten egg.
Stir dry ingredients into the creamed mixture until a soft dough forms; do not overmix.
Press the dough evenly into the prepared dish, covering the bottom and about halfway up the sides.
Melt 1 tbsp butter in a skillet over medium heat. Add apples and lemon juice; cook 2 minutes.
Stir in the sugars, cinnamon, and nutmeg. Cook until apples soften, 5–7 minutes, stirring often.
Whisk cornstarch with water. Pour into the skillet and simmer until thick and glossy, 1–2 minutes. Cool 5 minutes.
Spoon the apple filling into the cookie crust and smooth the top.
Combine oats, flour, brown sugar, cinnamon, and salt. Cut in cold butter until clumps form; scatter over apples.
Bake until the top is golden and the filling bubbles at the edges, 28–35 minutes. Cool 30–45 minutes before slicing.
Notes
Variation: Drizzle warm caramel over each slice and finish with a pinch of flaky salt. Serving tip: It’s fantastic slightly warm with a scoop of vanilla ice cream. Storage: Keep covered at room temperature for 1 day or refrigerate up to 4 days; reheat slices in a 300°F oven for 8–10 minutes.This recipe is an original creation inspired by classic Apple Cookie Pie Delights flavors. All ingredient ratios and instructions are independently developed.