Preheat the oven to 175°C (345°F) using conventional heat (no fan).
Butter and flour the pan. You can replace the flour with brown sugar for a slightly caramelized finish.
Wash the cherries, then dry them thoroughly.
Sift the flour and cornstarch, then add the sugar, a pinch of salt, and the lemon zest.
Mix everything together, then make a well in the center and add the whole eggs and egg yolks. Stir with a whisk gently, without beating vigorously, to avoid incorporating too much air.
Next, add the heavy cream and milk, and mix again until smooth. Add the vanilla extract at this stage if you're using it.
Place the cherries in the prepared pan, then gently pour the clafoutis batter over them.
Bake for 45 minutes to 1 hour. A skewer inserted in the center should come out clean.
The clafoutis will puff up during baking, like a cheesecake, then slightly deflate as it cools, this is completely normal.
Remove it from the oven and let it cool completely before unmolding. It can be enjoyed warm or cold and retains its perfect texture even two days later.