In a medium pot, bring the water and sugar to a boil. Add orange slices and cook for 10 minutes. Remove pot from the stove and let oranges cool in the water for mixture 90 minutes.
Remove oranges from the water mixture and place slices on parchment paper. Leave dry on the counter for 24 hours. After then, store in an airtight container with slices separated by parchment paper. Slice will keep for up to a month.
For the Cake...
Grease jelly jars with vegetable spray. Preheat oven to 300 degrees.
With an electric mixer, whisk eggs until fluffy. Add-in sugars and beat until well combined. Stir in remaining ingredients.
Pour slightly more than two fingers into each jelly jar. Place jars on baking pan and bake for 45 minutes.
For the Ganache...
Heat cream and chocolate over a double boiler. As the chocolate melts, whisk until well combined.
Pour warm ganache over cooled cakes. Garnish with an orange slice.
Notes
Here is a quick, fun tip. After removing the orange slices from the sugar/ water mixture, return to low heat for another 20-30 minutes. This will create a blood orange simple syrup perfect for your cocktails and mocktails.