Add flour and butter to a large bowl, and use your fingertips to rub butter into flour until mixture resembles coarse breadcrumbs with no large lumps of butter remaining.

Add the 1/4 cup Demerara sugar, egg yolks, sour cream, and brandy to flour mixture and combine with a spatula just until the dough comes together. Wrap dough in plastic wrap and chill for at least 2 hours or overnight.

Meanwhile, place apples, raisins, the 1/3 cup Demerara sugar, vanilla sugar, cinnamon, and lemon juice in a saucepan. Bring to a simmer over medium-low heat and simmer until apples are tender, and mixture is slightly thickened (about 10 minutes). Set aside to cool.

Preheat the oven to 400 degrees F (200 degrees C). Line a 9x16-inch baking pan with parchment.

Divide the chilled dough into two equal pieces. Roll the dough out on a lightly floured surface into 2 9x16-inch rectangles. Place one of the rectangles into the prepared baking pan.

Bake in the preheated oven until a pale crust develops on top, 10 to 15 minutes. Remove from the oven.

Carefully brush the semi-baked crust with apricot jam. Evenly distribute filling over the crust. Place the second rectangle of dough on top and prick it all over with a fork.

Bake until crust is lightly browned and filling is hot and bubbly, about 30 minutes.