Put the butter and chocolate in a small microwave-safe bowl and melt the mixture on high heat for 30 seconds. Check and stir and repeat once or twice until the butter and chocolate melt without bubbling or burning. (You can also do this step in a 1-quart pot over medium-low heat.) Stir with a soft spatula until the mixture is cool enough to touch.
Put the cherries and the chocolate mixture into a food processor fitted with a metal blade. Add 2 cups of the powdered sugar along with the vanilla, and salt. Let the machine run until the paste-like mixture is smooth and forms a ball. If a ball doesn’t form after a minute, add 1 tablespoon water through the feed tube. After that, add water 1 teaspoon at a time until you get a ball shape, careful not to add too much. You want the paste to be stiff enough to pinch with your fingers into a damp glob. Carefully take the blade out, scrape the paste into a large bowl, cover, and refrigerate for at least 1 hour or up to a day.
When you’re ready to roll the bonbons, put a sheet of parchment paper in a large rimmed baking sheet. Sprinkle the last 1/2 cup powdered sugar onto a plate and smash any clumps with a fork. Use your hands to grab and roll big pinches of the cold paste into 1-inch balls. Then roll them in the sugar so they’re coated all over and put them on the prepared pan. Use more as needed until all the paste is turned into bonbons. Enjoy your candy! Keep the leftovers in an airtight container in the refrigerator for up to a few days or in the freezer for several weeks.