I made these for the first time last year, and let me tell you, they bear absolutely no resemblance to the nasty plastic things that are found in supermarket jars (thank goodness).
It's possible that I posted the recipe last year--likely, even--but making it for the second time I've got some details to add.
Maraschino Cocktail Cherries Makes (3) 6 oz. jars
1 lb. pitted sour cherries [or (1) 24 oz. jar canned]
1/2 c. sugar
1/2 c. water, or, liquid from jar
2 tsp. lemon juice
1 cinnamon stick
2 strips of lemon zest
pinch freshly grated nutmeg
1 c. Maraschino liqueur
1/2 tsp. each vanilla and almond extracts
Combine all ingredients but cherries, liqueur, and extracts; bring to a rolling boil. Turn heat to medium and add the cherries. Simmer for 5 to 7 minutes. Remove pot from heat and add liqueur and extracts. Discard cinnamon and lemon zest (I composted them).
Fill jars about 4/5 full of cherries; pour in liquid, leaving a generous 1/2" headspace. The cherries will expand during the processing--if you don't leave enough space, you will have to take out some of the contents and re-process the jars!
Process for 10 minutes in a hot water bath. Leave jars undisturbed for at least 12 hours. Remove screw lids, wash and dry jars and lids. Put lids back on and tighten. Add labels.
If you used canned cherries you'll have extra juice & maybe extra liquid from making these. I combined all of this with some simple syrup and boiled it down to make sour cherries syrup. Boiled, it amounted to just about one cup. If you add a teaspoon or so of vodka, it can be kept, in a tightly closed jar, at room temperature. Use it for sodas, cocktails, or anything that takes your fancy.