Mix the jello and hot water together, stir until everything is dissolved and there are no grains of gelatin remaining. Add in the orange zest.
Pour the jello into a 9x13" tray and refrigerate until ready to assemble.
Whisk together the egg and sugar for 4-5 minutes until they get pale and fluffy.
Gently fold in the dry ingredients and divide the batter between 12 greased muffin cups.
Bake at 350F for 7-10 minutes or until the edges are golden brown and the tops set. Let cool completely.
Cut out circles of jelly so they are slightly smaller than the flat bottoms of the sponge cakes and lay them on top of the flat sides. I used a shot glass that I dipped in hot water, the water helps release the jelly from the glass and I used an off set spatula to scrap the jelly from the pan.
Melt the chocolate in the microwave for 15 seconds and then stir, repeat until the chocolate is fully melted.
Dollop some chocolate over the top of the orange jelly and spread it to the edges of the jelly. Push it to encourage it to fall over the edges.
Tap the cooking on edge of the bowl to flatten out the chocolate and help it drip over the side of the sponge cake.
Chill the jaffa cakes for a few minutes to set up the chocolate.