In a medium-size microwave-safe bowl (these Nordic prep and serve bowls are my favorite and I use them for everything) add ¼ cup melted butter.Pour in the semi-sweet chocolate chips and melt them in the microwave in 30-second intervals. Stir after each interval, and repeat until the chips are completely melted and smooth. Once the chocolate chips are melted and smooth, mix in 7 ounces of the condensed milk.Pour the chocolate mixture into an 8×8 inch baking pan that is lined with parchment paper. The parchment paper will allow the mixture to set and will make it a whole lot easier to get out of the pan.Place the pan with the chocolate mixture in the fridge and allow it to chill until the fudge is firm. It’ll take about 30 minutes for the chocolate fudge to set.
While you’re waiting on that to set, we can go ahead and do the same for the white chocolate and eggnog mixture. This will be poured on top of the other mixture to create the two layers.Take a medium-size microwave-safe bowl (luckily, my Nordic bowls come in a set of 4) and add ¼ cup melted butter.Just like we did with the semi-sweet chocolate, we are going to add in and melt white chocolate chips in the microwave in 30-second intervals.Remember to stir after each interval, until the white chocolate is completely melted and smooth. Once it’s melted, mix in 7 ounces of the condensed milk, then mix in the eggnog and the allspice.Now it’s time to bring the two together!Get the semi-sweet chocolate mixture out of the fridge and pour the eggnog mixture on top.If you choose to include the small marshmallows, sprinkle the marshmallow bits on the top. Press them in gently so that they stay in place.Put the pan back in the fridge until it is completely firm. It’ll take about 2 hours for everything to be set.