Line a 17½ × 12½-inch pan with parchment paper.
Melt all of the chocolate chips with the optional coconut oil until smooth. Pour about half into the pan for the bottom layer, spreading evenly. Chill until firm. Save the remaining chocolate and simply rewarm it later for the top layer.
Lightly scratch the surface of the chilled chocolate with a fork to help the nougat stick.
For the nougat, melt the butter in a saucepan. Stir in the sugar and heavy cream, bringing to a gentle boil for about 5 minutes while stirring. Remove from the heat and mix in the marshmallow creme, peanut butter, Biscoff cookie butter, vanilla, and salt until smooth. Spread over the chocolate layer.
Sprinkle the peanuts evenly over the nougat, then top with the crushed Biscoff cookies, gently pressing them into the nougat.
In a saucepan, melt the butter for the caramel. Stir in the brown sugar and sweetened condensed milk. Cook over medium heat, stirring constantly, until thickened and smooth (about 8–10 minutes). Remove from the heat and stir in the vanilla and salt. Pour over the peanut and cookie layer.
Chill until the caramel is set.
Rewarm the remaining chocolate and spread it evenly over the caramel.
Refrigerate for 2–3 hours, then let the pan sit at room temperature for 10–15 minutes before slicing for the cleanest cuts.
