Preheat your oven to 350°F (≈175°C).

In a mixing bowl, cream together the salted butter and granulated sugar until light and fluffy.

Add the vanilla extract and the egg white. Mix until they are well combined and the mixture is smooth.

Stir in the flour and baking powder. Mix thoroughly until you have a uniform cookie dough.

Roll out the dough on a lightly floured surface until it is about ¼ inch to ½ inch thick. Use a round cookie cutter to cut out circles of dough. Transfer the circles to an ungreased baking sheet or pan.

Bake at 350°F for 6–8 minutes, or until the cookies are puffy and no longer glossy (they should look set but not overbaked).

Remove the cookies from the oven and transfer them to a wire rack to cool completely.

While the cookies are cooling, melt the caramels and milk together: place the unwrapped caramels and milk in a microwave‑safe bowl, microwave on short bursts (30 seconds) stirring at each interval until the caramel is smooth and creamy.

Once the cookies are cool, carefully spoon a few teaspoons of the melted caramel onto each cookie, spreading toward the edges until it almost covers the surface.

Place the caramel‑topped cookies into the fridge for 10–15 minutes or until the caramel has set and is cold.

Melt the milk chocolate chips by microwaving on 30‑second intervals, stirring after each until fully melted and smooth.

Spread a small amount of the melted chocolate onto each caramel‑topped cookie, smoothing it over the top. Let the chocolate layer cool and set (you can return them to the fridge to speed this up).

Once the chocolate is set, your Twix Cookie Cups are ready to serve!