In a heavy-bottomed saucepan, mix the granulated sugar and water, stirring gently to moisten the sugar and ensuring no crystals stick to the sides. Add the light corn syrup to help prevent crystallization. Place the saucepan over medium-high heat and let it boil without stirring until the sugar dissolves and turns amber, which should take about 8-10 minutes. Be cautious as it can burn quickly.

While the sugar mixture is cooking, heat the heavy cream in the microwave for about 1 minute, being careful not to let it burn. Once the caramel reaches the amber color, remove it from heat and slowly pour in the heated cream while stirring constantly. Expect vigorous bubbling, so take care to avoid splatters. Stir until the caramel and cream are fully combined, then add the unsalted butter, vanilla extract, and salt, continuing to stir until the butter melts and the sauce is smooth. Allow the caramel to cool for a few minutes before transferring it to a heatproof container to cool completely.

Next, prepare the apple filling. In a large bowl, combine the diced apples, lemon juice, sugar, cinnamon, and a pinch of salt, tossing until the apples are evenly coated. Transfer this mixture to a medium-large pot over medium-high heat, stirring occasionally until the apples soften and release their juices, bringing it to a slow boil.

In a small bowl, mix the cornstarch with cold water to create a slurry. Once the apples have softened, add the slurry to the pot while stirring constantly. The mixture should thicken within 30 seconds; if it doesn't, you may need to add more slurry. Remove from heat and let the apple mixture cool completely before using. It can be stored in the refrigerator for up to a week.

In a large bowl, whisk together the cold milk and sweetened condensed milk until combined. It may look clumpy at first, which is normal. Sprinkle the instant vanilla pudding mix over the top and whisk until smooth and free of lumps, about 2-3 minutes. Let it sit for 5-10 minutes to thicken.

While the pudding thickens, prepare the whipped cream. In a stand mixer or using a handheld mixer, beat the heavy cream and vanilla extract on medium-high until stiff peaks form. Be careful not to overbeat; if it looks curdled, add a splash of cream and mix on low until it comes back together.

Gently fold the whipped cream into the pudding mixture using a rubber spatula, being careful not to deflate it.

To assemble, you can use individual cups, a large 9x13 casserole dish, or a trifle bowl. Start with a layer of the pudding mixture at the bottom, enough to coat the base. Add a layer of whole biscoff cookies on top, fitting them snugly without overlapping too much. Spoon about ½ cup of the apple filling over the cookies, followed by a generous drizzle of caramel, spreading it evenly to the edges. Repeat the layers of pudding, cookies, and apple filling until you run out of ingredients, aiming for 2-3 full layers.

Finish with a final layer of pudding that covers everything completely, sealing it against the sides of the dish to prevent the top layer of cookies from drying out. Press a sheet of plastic wrap directly against the surface of the pudding to prevent a skin from forming. Refrigerate for at least 6 hours, preferably overnight, to allow the cookies to soften.

Before serving, crush the reserved cookies into a mix of larger pieces and fine crumbs, then scatter them generously over the top. Add a few spoonfuls of apple pie filling on top and serve cold directly from the fridge.