Line an 8x8-inch pan with parchment paper, leaving extra overhang on two sides to create handles for lifting the bars out later.

Blend the cookies in a food processor until they form fine crumbs. Transfer to a mixing bowl and stir in the melted butter until the mixture resembles damp sand. Press the mixture firmly into the bottom of the pan using damp fingers. Refrigerate while preparing the caramel.

In a medium saucepan, melt the butter over medium heat until small bubbles appear around the edges. Add the brown sugar and whisk until it starts to boil and the sugar fully dissolves, about 2 minutes.

Whisk in the sweetened condensed milk and continue whisking over medium heat for 5 to 6 minutes, until the caramel thickens and turns slightly darker. Remove from heat and stir in the cookie spread and sea salt.

Pour the caramel over the chilled crust and gently shake the pan to level the surface. Return to the refrigerator and chill for 15 minutes.

Combine the chopped chocolate and cookie spread in a microwave-safe bowl. Microwave at 50% power for 1 minute, then stir. Continue microwaving in 30-second increments at 50% power, stirring each time, until smooth. This may take up to 5 minutes depending on the microwave.

Spoon the melted chocolate over the caramel layer and use the back of a spoon to smooth it out. Sprinkle sea salt over the top and refrigerate until fully set before slicing.