Step 1: Prepare the Fudge Base

1. Line an 8×8-inch baking dish with parchment paper, leaving an overhang for easy removal later.
2. In a medium saucepan, combine the white chocolate chips and sweetened condensed milk. Heat over low heat, stirring constantly until the chocolate is fully melted and the mixture is smooth.
3. Remove the saucepan from the heat and stir in the vanilla extract.

Step 2: Make the Cinnamon Swirl

1. In a small bowl, mix the melted butter, brown sugar, and ground cinnamon until combined. Set aside.

Step 3: Assemble the Fudge

1. Pour half of the fudge mixture into the prepared baking dish, spreading it evenly with a spatula.
2. Drizzle half of the cinnamon swirl mixture over the fudge, then use a knife or toothpick to swirl it gently into the fudge base.
3. Repeat with the remaining fudge mixture and cinnamon swirl, creating a layered and marbled effect.

Step 4: Chill the Fudge

1. Cover the dish with plastic wrap and refrigerate for at least 4 hours, or until the fudge is firm and set. For best results, let it chill overnight.

Step 5: Prepare the Icing Drizzle

1. In a small bowl, whisk together the powdered sugar, milk, and vanilla extract until smooth. Add more milk if needed to achieve a drizzle consistency.

Step 6: Add the Final Touches

1. Remove the fudge from the baking dish using the parchment paper overhang. Drizzle the icing over the top in a zigzag pattern.
2. Allow the icing to set for 10–15 minutes before slicing the fudge into squares.