Preheat oven to 375 °F and grease four 5-ounce baking dishes.
Cut plums into quarters and arrange in each baking dish. Combine flour, sugar, cinnamon and salt. In a separate bowl, whisk eggs, egg yolk, vanilla and milk.
Add milk mixture to flour and whisk until combined. Pour gently over plums and bake for 25 to 30 minutes, until puffed and golden.
Serve clafoutis warm or at room temperature with a scoop of ice cream and a drizzle of lavender honey.