In the bowl of a stand mixer fitted with the paddle attachment, beat butter, confectioners’ sugar, and salt at medium speed until light and creamy, 2 to3 minutes, stopping to scrape sides of bowl. Beat in vanilla.
In a medium bowl, whisk together flours. With mixer on low speed, add fl our mixture to butter mixture in two additions, beating just until combined after each addition.
Turn out dough, and shape into a disk. Wrap in plastic wrap, and refrigerate until firm, about 2 hours,or up to overnight.
Preheat oven to 325°F (170°C). Line baking sheetswith parchment paper.
On a lightly floured surface, roll dough to ½-inch thickness. Using a 4-inch tree-shaped cutter, cut dough, rerolling scraps as necessary. Place 1½ inches apart on prepared pans.
Bake until edges are lightly browned, 20 to25 minutes, rotating pans halfway through baking. Let cool on pans for 10 minutes. Remove from pans, and let cool completely on wire racks.
Spoon melted white chocolate into a piping bag, andcut a very small opening in tip. Pipe onto cookies to resemble garland; immediately garnish with nonpareils, if desired. Let stand until chocolate is set, about 1 hour. Store in an airtight container for up to 5 days.