Butter a medium baking dish, ~2-quart and at least 1 ½-inches deep.
Combine milk, ⅓ cup of the sugar, eggs, vanilla, salt and flour in a blender pitcher; blend until smooth and foamy, about 1 minute. Pour ¼-inch layer in to prepared baking dish and place in oven for 5 minutes, or until batter has set. Remove from oven.
Spread peach slices evenly over set batter. Sprinkle remaining sugar (~2 tablespoons) over peach slices. Pour on remaining batter. Bake in the center of the oven for 50-55 minutes, until the clafoutis is puffed and golden brown and a sharp knife or cake tester inserted into the center comes out clean. Remove from oven and let cool slightly.
Just before serving, spoon powdered sugar into a fine sieve or shaker and sprinkle over the clafoutis. Serve warm.