01 -
Line an 8-inch square baking pan with parchment paper.
02 -
Pulse the Biscoff cookies in a food processor until fine crumbs form. Add melted butter and salt, blending to fully combine. Transfer the mixture to the prepared pan and press firmly into an even layer using a measuring cup or glass. Refrigerate while preparing the caramel.
03 -
In a heavy-bottomed saucepan over low-medium heat, melt the butter. Stir in light brown sugar, mixing until dissolved and no longer gritty. Add sweetened condensed milk and increase the heat slightly. Cook, stirring constantly, until bubbles begin to appear and the mixture thickens to a deep golden color, about 5 to 7 minutes. The caramel should reach 225°F if using a thermometer.
04 -
Remove the saucepan from heat. Quickly stir in the Biscoff spread and sea salt until fully incorporated. Pour the hot caramel over the chilled cookie base, tilting the pan gently to create an even surface. Refrigerate for at least 15 minutes.
05 -
Melt the chopped milk chocolate in a microwave-safe bowl using 30-second intervals, stirring thoroughly after each, until 90% melted. Stir to melt completely from residual heat.
06 -
Microwave 1 tablespoon Biscoff spread for 15 to 20 seconds until fluid. Pour melted chocolate over the caramel layer, then drizzle the runny Biscoff spread on top. Use a knife to swirl, moving carefully to avoid disturbing the caramel.
07 -
Refrigerate the assembled shortbread for 1 to 2 hours or until fully set before slicing.