In a blender, combine eggs, milk, maple syrup, tapioca starch, salt, and vanilla.
Use a touch of the butter to wipe the inside of a shallow gratin pan or 9 inch pie plate, then add the butter to blender. Blend until smooth, 30 seconds.
Distribute berries evenly in pie plate and pour batter over top. Bake until puffed, a little brown, and just set in middle, 25 minutes. Remove from oven and let deflate, and cool. Refrigerate at least six hours or overnight. (see note above) Before serving, sprinkle with powdered sugar.
Bake this, and let it completely cool and refigerate overnight for it to be custard. Straight out of the oven it will look like a dutch baby, then deflate into a claufoutis. Still good, but I prefer it cold.