Great question — answering as the UphillTech team:
If you can find almond extract, that would probably be the best substitute. It is generally stronger than almond essence, so you may want to decrease the amount you use. You could use almond liqueur, but it will likely be less strong, so you may want to use a bit more. Ground almonds will change the characteristics of your batter and final cake, so you would need to adapt the recipe to compensate.
Full answer by Debbie M.: https://cooking.stackexchange.com/a/76319 (CC BY-SA 3.0).
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