Start by crushing the Lotus Biscoff biscuits into fine crumbs using a food processor or a ziplock bag and rolling pin. Combine the crumbs in a bowl with melted unsalted butter and a pinch of salt, mixing until the mixture resembles wet sand. Press this mixture into the bottom of a lined 8-inch square baking dish, ensuring it’s compact and even. Chill in the refrigerator for about 30 minutes to firm up.

In a heavy-based saucepan, melt unsalted butter over medium heat, stirring continuously. Once melted, mix in the light brown sugar and sweetened condensed milk, stirring constantly until the mixture thickens and turns a light golden color, about 5-7 minutes and reaching a temperature of 110°C (225°F). Remove from heat, then stir in the Lotus Biscoff spread and fine sea salt until smooth and well combined.

Pour the delicious caramel layer over the chilled biscuit base, using a spatula to spread it evenly to the edges. Gently tap the dish on the counter to remove any air bubbles and ensure a smooth layer. Allow the caramel to cool at room temperature for about 10 minutes before proceeding to the next step, ensuring it maintains its gooey texture.

Melt the milk chocolate in a heatproof bowl set over simmering water or in short bursts in the microwave, stirring until completely smooth. Once melted, drizzle the chocolate over the caramel layer, spreading it gently with a spatula for an even coating. Optionally, add dollops of Lotus Biscoff spread on top for a beautiful finish, swirling with the back of a spoon.

Refrigerate the assembled Biscoff Millionaires Shortbread for at least 2 hours, or until firm to the touch. Once set, remove from the fridge and let it sit at room temperature for 20 minutes before slicing into squares with a warm knife. Enjoy the delightful layers of cookie, caramel, and chocolate as you indulge in this no-bake treat!