Step 1: In a medium bowl, combine the graham cracker crumbs, granulated sugar, and melted unsalted butter. Mix thoroughly until the crumbs are evenly moistened and resemble wet sand.
Step 2: Press the mixture firmly and evenly into the bottom of a 9x13 inch baking dish. Use the back of a spoon or the bottom of a flat glass to compact it tightly. Place the crust in the freezer for at least 15 minutes while you prepare the other components.
Step 3: In a large skillet or pot, melt 2 tablespoons of butter over medium heat. Add the sliced apples and cook for 5-7 minutes, stirring occasionally, until they start to soften but still have a slight bite.
Step 4: Stir in the brown sugar, cinnamon, nutmeg, a pinch of salt, and lemon juice. Continue to cook for another 5-8 minutes, or until the apples are tender but not mushy, and the sauce has thickened slightly. Remove from heat and let the apple filling cool completely.
Step 5: In a large mixing bowl, beat the softened cream cheese and powdered sugar together with an electric mixer until smooth and creamy, about 2-3 minutes. Make sure there are no lumps.
Step 6: Add the milk and vanilla extract, and beat again until just combined. Gently fold in half of the whipped topping until no streaks remain. Be careful not to overmix.
Step 7: Remove the chilled graham cracker crust from the freezer. Spread half of the cream cheese mixture evenly over the crust.
Step 8: Carefully spoon and spread half of the cooled apple filling over the cream cheese layer.
Step 9: Repeat with the remaining cream cheese mixture, spreading it gently over the apple layer. Then, top with the remaining apple filling.
Step 10: Finally, spread the remaining whipped topping evenly over the top layer of apples. For a pretty finish, you can make swirls with the back of a spoon or sprinkle with extra cinnamon or crushed graham crackers.
Step 11: Cover the baking dish tightly with plastic wrap and refrigerate for at least 4-6 hours, or preferably overnight. Chilling is essential for the layers to set properly.
Step 12: Before serving, you can garnish with a dusting of cinnamon, a sprinkle of chopped pecans, or a drizzle of caramel sauce. Slice and serve cold. Store any leftovers in an airtight container in the refrigerator for up to 3-4 days.