How to Make It
In a 12-inch nonstick skillet, melt 1/2 tablespoon of the butter. Add the peaches, 1 tablespoon of the granulated sugar and the lemon juice and cook over high heat, stirring occasionally, until the peaches are tender and lightly browned, about 5 minutes. Transfer the peaches to a plate and clean the skillet.
In a large bowl, whisk the flour, milk, egg yolks, zest and 2 tablespoons of the granulated sugar until smooth. In another bowl, using an electric mixer, beat the egg whites with the salt until soft peaks form. Beat in the remaining 1 tablespoon of granulated sugar until the whites are glossy. Fold the whites into the batter until no streaks remain.
In the skillet, melt 1 tablespoon of the butter. Add the batter, cover and cook over moderately low heat until it is golden on the bottom and the top is beginning to set, 4 to 5 minutes. Slide the pancake onto a large plate. Carefully invert the skillet over the pancake. Using oven mitts, flip the skillet and the plate to return the pancake to the pan. Cook until the underside of the pancake is set and lightly browned, about 2 minutes.
Using a wooden or heatproof plastic spatula, cut the pancake in the skillet into 2-inch squares. Dot with the remaining 2 1/2 tablespoons of butter, sprinkle with the 1/3 cup of confectioners' sugar and top with the peaches. Cook, tossing, until the pancake is caramelized, about 5 minutes. Add the blackberries and toss until they are heated through, about 1 minute. Transfer the kaiserschmarrn to a platter, sprinkle with confectioners' sugar and serve.