Break chocolate pieces into a large microwaveable bowl and microwave in 30 second increments at 50% power until completely melted and smooth.
Stir in the sweetened condensed milk and orange extract (and orange zest, if you wish) until everything is combined and microwave on 50% power for another 45 seconds to 1 minute (stopping after 30 seconds to stir).
Line an 8-inch x 8-inch square baking pan with parchment paper and pour the fudge mixture into the lined pan, smoothing out the top.
Chill the fudge in the refrigerator for one to 4 hours, or until completely set.
Slice into small squares, garnish with some additional orange zest or orange slices (I like to dip my orange slices in sugar before garnishing!) and serve.
This fudge freezes well and it can be stored in the fridge for up to 3 days in an airtight container.