Line an 8-inch x 8-inch baking dish with foil, pressing it into all of the corners and allowing it to hang over the edges a bit. Set aside.
Place the white chocolate chips in a mixing bowl and set aside.
Pour the sweetened condensed milk into a microwave safe bowl and heat in the microwave for 90 seconds.
Carefully remove the bowl and immediately pour the milk over the chocolate chips. Allow the chocolate chip to melt for 1 minute before stirring. Stir until combined and smooth.
Pour in the rum extract and butter and add a pinch of salt. Carefully mix until completely combined. Taste the fudge and adjust the rum extract (adding more as needed) until the flavor is to your liking.
Pour the fudge mixture into the prepared dish. Use a rubber or offset spatula to smooth the fudge into an even layer. Tap the dish on the table a couple times to remove any bubbles.
Sprinkle a light dusting of cinnamon all over the top of the fudge.
Refrigerate for 2-4 hours, or until the fudge has set. Remove the fudge from the fridge and cut into 36 pieces.
Notes
Refrigerator storage : This is a great treat to make ahead of time and package as gifts for the holiday season. Stored in an airtight container in the fridge it will last for 3-4 weeks.Freezer storage: While you technically can freeze fudge, it will change the texture and can become grainy. If you want to give it a try, wrap tightly in a few layers of plastic wrap and place into a freezer bag. Thaw at room temperature.Keep in mind that rum extract, used in this recipe, will likely contain alcohol. I recommend enjoying this fudge as an adults only treat.