Preheat the oven to 375 degrees F. Butter a 12-inch round baking dish or pie plate.
Combine the egg yolks and 1/3 cup of the granulated sugar in a large bowl. Using a handheld mixer, beat on medium-high speed until ribbons form when you lift the beater just slightly out of the batter, about 8 minutes. Add the heavy cream, flour and vanilla extract. Reduce the speed to low and beat until thoroughly blended, stopping the mixer occasionally to scrape down the sides of the bowl with a rubber spatula.
Put the prepared baking dish on a baking sheet and slide into the oven to preheat for 4 to 5 minutes.
Meanwhile, whisk together the egg whites and salt in a small bowl for about 30 seconds. Add to the batter and beat with the mixer on low speed until just incorporated, 1 to 2 minutes.
Combine the cherries, lemon zest and remaining 1/3 cup granulated sugar in a medium bowl and stir until the cherries are thoroughly coated. If using frozen cherries, mix in 1 tablespoon of flour.
Remove the baking sheet from the oven, pour the cherry mixture into the baking dish and top with the batter. Bake until set in the middle, 30 to 35 minutes. Serve warm with confectioners' sugar and a small dollop of whipped cream.