Preheat the oven to 400F. Spread the pitted cherries out on a parchment-lined baking sheet, sprinkle them with 1/4 cup sugar and roast for 15-20 minutes, stirring once or twice, until soft and juicy-watch it toward the end, so that the edge of the sticky syrup doesn't start to burn. Scrape into a bowl and set aside to cool - if you like, mash them with your spatula or potato masher to rough them up a bit.
Meanwhile, heat both creams in a large saucepan over medium-high heat. In a small bowl, whisk together the egg yolks and the remaining 1/2 cup of sugar. When the cream is steaming, whisk a ladle of hot cream into the yolk mixture, then whisk it back into the saucepan of cream, whisking briskly until the mixture comes to a boil. Reduce the heat and cook, stirring, for a minute or two, then remove from the heat and stir in the vanilla and salt. Set aside to cool, then cover and refrigerate for a few hours, or overnight.
Churn the cold custard in your ice cream machine according to the manufacturer's directions until it's the consistency of soft ice cream; with the motor running, add the cherries and any syrup that has accumulated in the bottom of the bowl. If you like, scrape into a bowl, container or loaf pan, cover and freeze to firm it up a bit more. Makes about 1 1/2L.