Combine the graham cracker crumbs with the melted butter in a bowl. Mix thoroughly with a fork to make sure every crumb is well coated, as this helps the crust hold together when pressed into the dish.

Transfer the buttered graham cracker mixture into a 9-inch pie dish. Press the crumbs evenly across the bottom and up the sides using your hands, then use the bottom of a kitchen glass to firmly press the crust into place, starting from the center and working outwards for an even thickness.

In a large saucepan over medium-high heat, combine the lemon gelatin dessert mix, apple pie spice blend, 1 1/2 cups water, and the thinly sliced apples. Stir until all the apple slices are thoroughly coated. Bring the mixture to a boil, then lower the heat to medium-low and cover. Simmer for 8 to 12 minutes or until the apples become tender, stirring occasionally to prevent sticking.

In a medium bowl, whisk together the vanilla pudding mix and 1/4 cup water until smooth. Pour this pudding mixture into the saucepan with the cooked apple mixture and stir to combine. You should see the mixture thicken almost immediately. Continue to cook over medium-low heat, stirring occasionally, for about 1 minute until fully thickened. I always keep an eye on the consistency here—if it looks a little too thick, just add a splash more water.

Pour the hot apple-pudding mixture into the prepared graham cracker crust, spreading it evenly. Let the pie sit at room temperature for about 5 minutes to set slightly before transferring to the refrigerator. Chill for at least 3 hours to allow the filling to fully set before serving.

Once the pie is well-chilled and set, top generously with whipped topping before slicing and serving. I like to add an extra dollop of whipped topping to each slice for a special touch!