Lightly grease and line a 20cm (8in) square shallow cake tin.
Pour 395g (14oz) tin condensed milk into in the microwavable container. Then add 200g (7oz) chopped dark chocolate, 200g (7oz) chopped milk chocolate, and 60g (2½ oz) diced butter, to the container (do not stir).
Place the lid onto the container and cook in the microwave on full power for 1 minute. Remove from the microwave and stir.
Return the container covered to the microwave and cook for a further minute. Stir again then repeat twice more, so that the fudge has had 4 minutes in the microwave.
Now repeat stirring well after every 30 seconds. For another 1-2 minutes until the mixture is starting to bubble around the edges of the container.
Then cook the fudge in the microwave for two more 30 second periods, stirring well between each.
Remove the container from the microwave and stir well. You will notice a thin layer of melted butter on the surface of the fudge. Set aside for 5 – 10 minutes to cool slightly.
Once the fudge mixture has cooled slightly, add ½ tsp orange extract. Stir it in thoroughly. The mixture should be thick and silky at this stage, and the melted butter should be incorporated following the thorough mixing.
Carefully pour the fudge into the tin (remember, it will still be very hot). Use the back of a metal spoon to coax it into the corners and level the top. Set aside to cool.
Once cool enough, cover with cling film and place into the fridge place into the fridge for a couple of hours, or over night, to firm up. Remove from the fridge and use a sharp knife to slice into pieces.