I suggest using thermomade condensed milk and using it immediately after making it. It will be warm and will make it much quicker and easier.
Place ¼ of the hot condensed milk into a jug or bowl. Set aside.
Leave the remaining ¾ condensed milk in the tmx bowl and add the milk/dark chocolate. Mix on speed 3 until melted. This should only take about 30 seconds. If you are using canned condensed milk you will need to heat at 50 degrees until melted.
Pour ¾ of this milk/dark chocolate fudge mix into the pan. Set aside the remaining ¼.
In the bowl of hot condensed milk that was previously set aside, add the white chocolate and mix until smooth. I find a fork works well. You may need to microwave it for 20 secs. Add the food dye and peppermint essence/oil and mix until combined.
Spoon peppermint fudge into the pan on top of the milk/dark fudge mix in dollops. It can be very rustic. Top with remaining milk/dark chocolate fudge.