We drew baking inspiration from Vienna's charming markets and enchanting Alpine traditions for these beautiful and festive viennese holiday cookies.
, at room temperature
apricot or raspberry
LINE 2 large baking sheets with parchment. Set aside.
STIR flour with salt in a medium bowl. Beat butter with mascarpone and icing sugar in a stand mixer on medium-high, until pale and fluffy, 4 to 5 min. Beat in egg yolks and vanilla, scraping down sides of bowl if needed, until smooth, about 1 min. Reduce speed to low. Gradually add flour mixture until combined. Scrape dough onto a lightly floured counter and divide in half. Using a floured rolling pin, roll each piece to 1/4 in. thick. Trim edges to make a 12-in. square. Roll onto rolling pin and transfer to a prepared baking sheet (dough may go up sides of sheet). Freeze until firm, 15 to 30 min. Repeat with remaining dough.
PREHEAT oven to 350F. Stir egg whites with water. Remove dough from freezer. Slice dough down the middle, both ways, to make 4 squares. Slice each square down the middle, both ways, to make 4 more. You should have 16 squares. Arrange squares on baking sheets 1 in. apart. With a sharp paring knife, make a 1 1/2-in. cut diagonally from each corner of each square toward the centre (do not cut all the way to the centre). Dab corners with egg white. Spoon 1 tsp jam in the centre of each square. Fold every other corner tip of dough into the centre to form a pinwheel, sealing with egg whites and pressing tips to hold together. Repeat for all squares. Brush tops of cookies with egg whites, then sprinkle with coarse sugar.
BAKE in centre of oven, until cookies are golden, 20 to 22 min. Let cookies cool on sheets 1 min, then transfer to a wire rack to cool completely. Repeat with remaining dough and jam. Store cookies in an airtight container up to 1 week or freeze at least 1 month. (Prep tip: Dough must be very cold in order to get perfectly straight edges. Return dough to freezer to chill as needed.)