Tex-Mex Chocolate Icebox Cookies

In a medium bowl, whisk together the first 6 ingredients and set aside. In the bowl of a stand mixer fitted with the whip attachment, beat together the sugar, egg, and vanilla on high speed until thick and pale, about 3 minutes. Add the butter and continue beating until smooth, about 3 minutes more. Use your fingers to work the reserved dry ingredients into the butter mixture until just combined.

Using a plastic bowl scraper, divide the dough in half and transfer each half to a large sheet of parchment paper. Use the paper to squeeze and roll the dough into 2 compact 9-inch logs, twisting the ends tightly to make uniform cylinders. Freeze for at least 8 hours and up to 30 days. (If freezing longer than 24 hours, wrap the paper-wrapped cylinders tightly in plastic.)

Preheat the oven to 350°F.

Meanwhile, unwrap and slice each log into ⅓-inch-thick rounds. Space the cookies ½ inch apart on parchment-paper-lined baking sheets, and bake until slightly puffed with tiny cracks on the surface, 7-9 minutes. Transfer to a wire rack to cool completely.

Place the rack of cooled cookies over a cool baking sheet. Using the tines of a small fork or a pastry bag fitted with a very fine tip, drizzle generously with melted white chocolate. Set the rack of cookies aside until the chocolate is firm. Stored in an airtight container, the cookies will keep for up to 7 days.