Preheat oven to 350 °F (180 °C).

Prepare the strudel dough according to the basic recipe.

Remove the crusts from the rolls, cut into small pieces and saturate with milk.

Cream the butter with confectioner’s sugar.

Fold in the bread, egg yolks, cornstarch, vanilla sugar, sour cream, and lemon zest.

Begin to beat the egg whites and then beat them to stiff peaks with the granulated sugar.

Carefully fold in the egg whites.

Lay a cloth on the work surface and flour evenly.

Lightly flour the dough as well and place on the cloth.

With a rolling pin, roll the dough out as thinly as possible.

Then slide both hands under the dough, palms down, and slowly stretch it in all directions, until it’s so thin that you could read a newspaper through it.

Be very careful not to tear the dough.

Saturate the dough with ¾ of the butter.

Lay the filling on the dough in a strip.

With the help of the cloth, fold the dough over the filling and then fold around once.

Cut off extra.

Place the strudel with the seam down on a buttered baking sheet and brush with the rest of the butter.

Bake for about 30 minutes.

For the Royale, mix all the ingredients together, pour over the strudel, and bake for another 20 minutes, lowering the oven heat to 320 °F (160 °C).

Dust with confectioner’s sugar and serve while still warm.