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

2. Add the white chocolate chips, sweetened condensed milk, eggnog, and butter to a medium saucepan.

3. Warm the mixture over low heat, stirring often, until the chocolate is fully melted and the mixture looks smooth and glossy.

4. Remove the pan from the heat and stir in the vanilla extract, ground nutmeg, salt, and rum extract if using.

5. Pour the fudge mixture into the prepared pan and smooth the top with a spatula.

6. Sprinkle a small pinch of ground nutmeg over the top.

7. Refrigerate for at least 3 hours, or until the fudge is firm in the center.

8. Lift the fudge from the pan using the parchment paper, then slice into small squares.

9. Serve chilled or store in an airtight container in the refrigerator.