Add the cherries, sugar, and lemon juice to a saucepan. Cook over medium heat for 5 to 7 minutes, until the cherries soften and release their juices.
Transfer the cherries to a bowl with a slotted spoon and refrigerate. Let the cherry syrup cool slightly.
Whisk the egg yolks and sugar in a heat-safe bowl until pale and slightly thickened.
Stir the heavy cream, whole milk, salt, and cherry syrup together in the saucepan. Warm over medium heat until steaming but not boiling.
Slowly whisk the warm cream mixture into the egg yolks. Return everything to the saucepan and cook over medium-low heat, stirring constantly, until the custard reaches about 170°F (75°C) and coats the back of a spoon.
Remove from the heat and stir in the vanilla. Strain the custard into a clean bowl, cover, and refrigerate until completely chilled, at least 3 hours.
Churn the chilled custard in an ice cream maker according to the manufacturer's instructions. Add the chilled cherries during the final few minutes of churning.
Layer the ice cream and cherry jam in a freezer-safe container, then gently swirl with a knife or spoon.
Cover and freeze for at least 4 hours, or until firm enough to scoop.