Prepare a gratin dish, about 9 by 5 by 2 inches, or a 10-inch round deep pie plate or porcelain dish, by smearing it with butter, just a teaspoon or so.
Dust it with flour, rotating pan so flour sticks to all the butter; invert dish to get rid of excess.
In a large bowl, whisk eggs until frothy.
Add granulated sugar and salt and whisk until combined.
Add cream and milk and whisk until smooth.
Add 1/2 cup flour and stir just to combine.
Layer clementine sections in dish; they should come just about to the top.
Pour batter over fruit to as close to top of dish as you dare; you may have a little leftover batter, depending on size of your dish.
Bake for about 40 minutes, or until clafoutis is nicely browned on top and a knife inserted into it comes out clean.
Sift some powdered sugar over it and serve warm or at room temperature.
Clafoutis does not keep; serve within a couple of hours of making it.