Preheat oven to 355F and prepare a baking dish or a cast iron pan - layer half of the sliced peaches on the bottom of the dish/pan.

Whisk together eggs, egg yolks, and fine sugar, then slowly add in the flour until you get a smooth batter.

Whisk in ilk and rum or brandy, if using. You'll get something resembling a light pancake batter.

Pour the batter over the peaches in the dish/pan then, carefully place the remaining peaches on top and sprinkle with vanilla sugar (optional).

Bake for 40 minutes until set in the middle, and the clafoutis is just on its way to turning golden brown.