Start by spraying your pan with cooking spray and cover bottom and sides of the pan with parchment paper. Once done, set aside. Grab a medium-size bowl and add in the butter and white chocolate chips. Place in the microwave and melt in 30-second bursts until totally melted and smooth. (Make certain that you don't cook for more than 30 seconds at a time or the mixture will burn)
Once melted and smooth, mix the salt and mint extract into the melted mixture.
Add your instant pudding mix and milk into a small bowl and whisk until it's smooth. (It will be thicker than regular pudding at this point)
Take your mixture and fold it into the melted chocolate.
Next, slowly add in the powdered sugar at about ¾ cup at a time. You can easily do this step with a spoon or hand mixer if you want. Continue to add in powdered sugar until the mixture is smooth and you have that fudge consistency that you're going for. If it appears too thick, all you need to do is add a tablespoon of milk. If it appears too runny, simply add in 1-2 tablespoons of powdered sugar.
Once done, take and separate the mixture between two bowls, evenly. Take your green food coloring and add to one bowl. Add by 1-2 drops at a time.
Using a spoon, take turns adding a layer of green fudge and white fudge until the bottom of the pan is covered. Then, take a knife/chopstick/skewer and mix the mixture up and down in swirls. Repeat until the fudge mixture is done.
Once done, put sprinkles on top and cover with foil. Place in the fridge until the fudge is firm.
Once firm, cut and enjoy!