Preheat the oven to 180°C (fan 160°C). Line a 20cm square baking tin with baking parchment, leaving some overhang for easy lifting later. You should hear a gentle hiss from the oven once it reaches temperature.

Make the biscuit base: In a large mixing bowl, combine the crushed digestive biscuits with the melted butter. Stir until every crumb looks damp and darkens slightly in colour. Press this mixture firmly into the base of your lined tin using the back of a spoon — you want a compact, even layer that feels solid to the touch.

Prepare the caramel filling: In the same bowl (saving on washing up), whisk together the sweetened condensed milk, light brown sugar, eggs, and vanilla extract until the mixture looks pale golden and feels smooth between your fingers when you test a tiny bit. The sugar should be completely dissolved — you shouldn't feel any grittiness.

Add the Biscoff spread: Warm the Biscoff spread in the microwave for 20 seconds until it becomes runny. Pour it into the caramel mixture and whisk until fully combined. The mixture will turn a deeper caramel colour and smell wonderfully spiced.

Pour and layer: Carefully pour the Biscoff caramel mixture over the biscuit base. Sprinkle the chopped dark chocolate evenly across the top — it should look like dark freckles against the golden caramel. Scatter over the crushed Biscoff biscuits for texture.

Bake to perfection: Place the tin in the preheated oven and bake for 22-25 minutes. The edges should look set and slightly darker in colour, while the centre should still have a gentle wobble when you shake the tin gently. The smell in your kitchen will be absolutely intoxicating — warm caramel and spiced biscuits.

Cool completely: Remove from the oven and leave to cool in the tin for 20 minutes at room temperature. Then transfer to the fridge for at least 2 hours — this is crucial. The bars need this time to set properly. You'll know they're ready when the surface feels firm to a gentle touch and the edges pull away slightly from the parchment.

Slice and serve: Lift the whole slab out using the parchment overhang. Place on a cutting board and slice into 16 even bars with a sharp knife. Wipe the blade clean between cuts for neat edges. The bars should have a clean, sharp cut with a visible layer of biscuit base and a glossy caramel top.