Prep the pan: Line an 8x8-inch baking pan with parchment, leaving overhang on two sides. This makes it easy to lift out and slice.

Crush the cookies: Add cookies or grahams to a zip-top bag and crush with a rolling pin until you have fine crumbs with a few small bits. You can also use a food processor. Aim for sandy, not powdery.

Make the chocolate base: In a medium saucepan over low heat, melt the butter (or coconut oil) and chocolate chips together, stirring until smooth. Remove from heat and whisk in the nut butter and sweetener until glossy.

Flavor it: Stir in vanilla, fine sea salt, and cocoa powder. Mix until fully combined with no streaks. The mixture should be thick but pourable.

Combine: Add the cookie crumbs to the chocolate mixture and stir until every crumb is coated. If using nuts or mini chips, fold them in now.

Press and level: Transfer the mixture to the lined pan. Press firmly with a spatula or the bottom of a measuring cup to create an even, compact layer. Sprinkle with flaky salt if you like.

Chill: Refrigerate for at least 2 hours, or freeze for 45–60 minutes, until set and sliceable.

Slice and serve: Use the parchment overhang to lift the block out. Cut into 16 squares with a sharp knife. Wipe the knife between cuts for clean edges.