Prepare the batter base: In a large bowl, whisk together the flour, egg yolks, milk, vanilla, lemon zest and salt until you have a smooth, pourable consistency — it should coat the back of a spoon with a silky sheen. No lumps should remain; if they do, press them against the side of the bowl with your whisk.

Whip the egg whites: In a clean, dry bowl, beat the egg whites with an electric mixer on medium speed until soft peaks form — the foam should look like a cloud of marshmallow fluff, and when you lift the whisk, the peak should droop gently. Gradually add the caster sugar, a tablespoon at a time, and continue beating until stiff, glossy peaks stand upright without collapsing.

Fold gently: Take a large spoonful of the whipped whites and stir it into the batter to loosen it, then tip the remaining whites on top. Using a large metal spoon, cut through the centre and fold the batter over the whites in a sweeping motion, turning the bowl as you go. Stop when you can no longer see streaks of white — the mixture should feel light and airy, almost like a soufflé batter.

Cook the pancake: Place a 25cm ovenproof skillet over a medium heat and add half the butter. When it sizzles and turns a nutty brown, pour in the batter and spread it into an even layer. Let it cook undisturbed for 3–4 minutes, until the bottom is a deep golden brown and the edges begin to lift from the pan. The top will still look slightly wet and bubbly.

Flip and tear: Slide the pancake onto a plate, then invert the skillet over the plate and flip it back into the pan — the cooked side should now be facing up. Dot the remaining butter over the surface, then use two forks to tear the pancake into ragged, bite-sized pieces. The sound of the forks breaking through the golden crust is your cue that it’s ready.

Caramelise the edges: Continue cooking over medium heat for another 2–3 minutes, stirring occasionally, until the torn pieces are crisp and deeply caramelised in places. You should see patches of dark amber where the sugar has caught — that’s where the flavour lives. Sprinkle with a tablespoon of icing sugar and toss once more to create a light glaze.

Finish and serve: Transfer the Kaiserschmarrn to warm plates, piling it high in a casual, rustic mound. Dust generously with the remaining icing sugar, scatter over the berries, and add a spoonful of clotted cream if you like. Serve immediately while the pieces are still crisp on the outside and pillow-soft within.