1. Line an 8-inch square pan with parchment paper, leaving overhang on the sides for easy removal.

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

3. In a saucepan over low heat, combine the white chocolate chips, sweetened condensed milk, remaining 3 tablespoons butter, vanilla extract, and salt. Stir until fully melted and smooth.

4. Pour half of the fudge mixture into the prepared pan. Spoon over half of the cinnamon mixture. Add the remaining fudge mixture on top, then finish with the rest of the cinnamon mixture.

5. Use a knife to gently swirl the cinnamon mixture through the fudge.

6. Refrigerate for at least 3 hours, or until fully set.

7. Whisk the powdered sugar and heavy cream together until smooth, then drizzle over the chilled fudge.

8. Lift the fudge from the pan, slice into squares, and serve.