Heat the sweetened condensed milk in a microwave-safe bowl for about 60 seconds, until warm.

Add the white chocolate and let sit for 1 minute, then stir until a thick, smooth fudge forms.

Crush the graham crackers and fold them into the white chocolate mixture. The mixture will be very thick.

Press the graham cracker fudge firmly into a parchment-lined square pan. Transfer to the refrigerator to chill while preparing the chocolate layer.

Heat the remaining sweetened condensed milk for about 90 seconds, until warm.

Add the chocolate and let sit for 2 minutes, then stir until completely smooth.

Pour the chocolate fudge evenly over the chilled graham cracker base, smoothing the top.

Refrigerate (or freeze) the fudge for 1–2 hours, until fully set.

Spread marshmallow fluff evenly over the top using a rubber spatula.

Using a kitchen torch on low, toast the marshmallow until golden brown.

No torch? Place the pan under a low broil setting for 1–2 minutes, watching closely.

Once set, remove the fudge from the pan and cut into a 4×4 grid (16 bars) using a sharp stainless-steel knife.

Enjoy fresh, or store covered in the refrigerator for up to 12 days.