In the bowl of a stand mixer fitted with the paddle attachment, beat butter at medium speed until smooth, 1 to 2 minutes. Add sugars, ground co ee, salt, and orange zest; beat at medium-low speed until smooth, about 1 minute. Add egg yolk and vanilla. Beat until combined, about 1 minute. With mixer on low speed, add our to butter mixture in two additions, beating until combined. Shape dough into a 12-inch log; wrap in plastic wrap, and refrigerate until firm, at least 2 hours.
Preheat oven to 325°. Line 2 rimmed baking sheets with parchment paper.
Using a serrated knife, cut dough crosswise into ¼-inch-thick rounds. Place at least 1 inch apart on prepared pans.
Bake until tops are set and bottoms are lightly golden, 15 to 18 minutes. Let cool on pans for 1 minute. Remove from pans, and let cool completely on a wire rack.
In a small microwave-safe bowl, heat chocolate on high in 10-second intervals, stirring between each, until melted and smooth (1 to 11/2 minutes total). Stir in shortening until smooth and well combined. Spoon chocolate mixture into a small pastry bag or resealable plastic bag; cut a 1⁄4-inch opening in tip or corner. Drizzle chocolate mixture over shortbread as desired. Let stand until set before serving, 15 to 20 minutes.
Recipe by Paula Deen Magazine at https://pauladeenmagazine.com/upgrade-your-holiday-baking-with-swans-down-cake-flour/