In a large, microwave-safe bowl, combine the white chocolate chips, nutmeg, cinnamon, ginger, and the sweetened condensed milk. Heat in 30-second increments, stirring in between each, until the white chocolate chips have melted.
Line an 8x8 baking dish with parchment paper and pour fudge into the pan, smoothing over the top.
Add some red and green sprinkles to the top of the fudge.
Place the pan in the fridge for at least 1-2 hours before cutting into squares and serving. The fudge should be firm before cutting.