• Prepare a tray by brushing it with a few drops of neutral flavoured oil or a quick spritz of cake release spray. Alternatively line with parchment paper.

  (If you are making a single batch of fudge, a regular takeaway tray is the ideal size! If making a larger batch, either use two trays, or a 7–8" (18–20 cm) square pan.) 
• Pour the condensed milk into a microwave-proof bowl, break up the chocolate into squares, and add along with the marmalade (reserving 6 slices for decoration).
• Put it in the microwave for 30 second bursts, until the chocolate is melted. The time taken will vary according to the power of your microwave.

  Go slowly, as you only want to melt the chocolate, not boil the mixture.
• Stir the hot condensed milk and melted chocolate together until smooth. Add the marmalade and stir it in.
• Cut each of the reserved pieces of chocolate orange into 4–5 pieces and set to one side.
• Pour the fudge into the prepared tray, and smooth the top. Decorate by arranging the reserved pieces of chocolate orange on top, lightly pressing them in.

  Place in the fridge for at least four hours, or overnight to set.
• Once set, flex the sides of the container to release the fudge. If you turn it upside down and give it a good tap it should fall out. Otherwise, pop it in the freezer for 10 minutes and it should come out easily.
• Cut into about 18–24 pieces square pieces. This is far easier with a big heavy knife. Store in the fridge in a lidded container.

To make on the stove top

• Prepare your trays as above.
• Pour the condensed milk into a saucepan, break up the chocolate into squares, and add along with the chocolate orange (reserving 6 slices for decoration).
• Warm the pan on the lowest heat (it might help to have a diffuser ring) and once the chocolate starts to melt, keep stirring it. Do not leave the pan, as it can rapidly overheat. If this happens, the mixture will split, spoiling your fudge. 
• Once the chocolate is melted and well combined with the milk, add the marmalade and stir it in well. 
• Pour the fudge into the tray. Smooth out and decorate with the reserved chocolate. Once cool, pop into the fridge to set for 4 hours or overnight.