Line an 8x8-inch baking dish with foil, leaving a slight overhang on the sides for easy removal.
Set the prepared baking dish aside.
To prepare the caramel layer, place the white chocolate chips and unsalted butter in a saucepan over low to medium heat.
Heat gently, stirring frequently, until the white chocolate chips and butter have melted and the mixture is smooth.
Add the dulce de leche to the melted white chocolate mixture.
Stir until fully combined and creamy.
Add the marshmallow cream.
Continue stirring until the mixture is smooth and evenly blended.
Pour the caramel mixture into the prepared baking dish.
Spread it into an even layer.
Place the pan in the refrigerator for 30 minutes, or until the caramel layer is slightly set.
To prepare the coffee layer, stir the instant coffee and hot water together in a small bowl until the coffee is fully dissolved.
Add the dissolved coffee mixture to the sweetened condensed milk.
Stir thoroughly until evenly combined, then set aside.
Place the white chocolate chips and unsalted butter for the coffee layer in a clean saucepan over low to medium heat.
Heat gently, stirring frequently, until melted and smooth.
Add the coffee-flavored sweetened condensed milk to the melted white chocolate mixture.
Stir until the mixture is smooth and creamy.
Add the marshmallow cream.
Continue stirring until fully incorporated and creamy.
Pour the coffee mixture evenly over the slightly set caramel layer.
Spread gently with a spatula, taking care not to disturb the caramel layer underneath.
Place the pan in the refrigerator and chill for at least 4 hours, or overnight, until fully set.
Once set, remove the fudge from the pan using the foil overhang.
Peel the foil away from the fudge.
Using a hot knife, cut the fudge into 36 squares.
Allow the fudge squares to come to room temperature before adding the chocolate drizzle.
Place the dark chocolate melting wafers in a microwave-safe bowl.
Microwave for 30 seconds, then stir until smooth.
If needed, microwave for an additional 15 seconds and stir again until fully melted.
Transfer the melted chocolate to a small zip-top bag.
Cut a small tip from one corner of the bag.
Drizzle the melted dark chocolate over the fudge squares.
Allow the chocolate drizzle to set completely.
Store the fudge in a sealed container at room temperature.