Stone the cherries with a cherry pitter. Place them in a large heavy-bottomed pot. Add the sugar, stir gently, and bring to a boil. Cook gently for about 15 to 20 minutes, the liquid should start to look like a light syrup.
Add lemon juice, alcohol, vanilla extract, and bitter almond flavor. Continue cooking for 10 more minutes. Remove the foam.
Divide the cherries between the sterilized jars and cover them completely with the liquid. Seal well and let cool. Keep in a dark cool place and let steep for about 3-4 weeks before serving. Once you open a jar, keep it refrigerated.
Always use to taste, too much can be overpowering. If using bitter almond essence (which is stronger), start with 3-4 drops and only add more (if necessary) after tasting.