Prepare the cherries: Wash, pit, and roughly chop the cherries.

1. Cook the cherries: In a large pot, combine the cherries and lemon juice. Add just enough water to cover the cherries (about 1/2 cup). Bring to a boil, then reduce heat and simmer for 10-15 minutes, until the cherries are soft.

2. Strain the juice: Place a fine-mesh strainer or cheesecloth over a bowl. Pour the cooked cherries into the strainer and let the juice drip through. Do not press the pulp, as this can make the jelly cloudy. You should have about 3-4 cups of cherry juice.

3. Prepare the jelly: In a clean pot, combine the cherry juice and pectin. Add the butter (if using) to reduce foaming. Bring the mixture to a full rolling boil over high heat, stirring constantly.

4. Add the sugar: Once boiling, add the sugar all at once. Return to a full boil and let it boil hard for 1-2 minutes, stirring constantly.

5. Test for doneness: To check if the jelly is ready, use a spoon to scoop a small amount and let it cool slightly. If it gels and holds its shape, it’s done. If not, boil for another minute and test again.

6. Skim off foam: Use a spoon to skim off any foam from the surface of the jelly.

7. Jar the jelly: Carefully pour the hot jelly into sterilized jars, leaving 1/4-inch headspace. Wipe the rims clean, then seal with sterilized lids and rings.

8. Process the jars: Process the jars in a boiling water bath for 10 minutes to ensure a proper seal. Remove and let cool completely. Check the seals before storing.