01 -
Whisk sugar, flour, and salt in a medium saucepan. Gradually whisk in eggnog until smooth. Cook over medium heat, whisking constantly, for about 8 minutes until the mixture is very thick and paste-like, and pulls away from the sides when pushed with a whisk. Transfer to a wide bowl, cover with plastic wrap, and refrigerate for 30 minutes. Let it return to roughly room temperature before using.
02 -
Beat softened butter with granulated sugar, condensed milk, powdered sugar, cream, vanilla, cinnamon, nutmeg, salt, and baking powder in a large bowl with a mixer on medium-low speed until smooth. Gradually beat in the flour on low speed until a soft dough forms, scraping the bottom of the bowl with a spatula to ensure even mixing. Keep the dough covered between batches.
03 -
Place sanding sugar in a small bowl. Roll dough into tablespoon-size balls and roll each in sanding sugar. Arrange 2 inches apart on parchment-lined cookie sheets. Dip the bottom of a glass in sanding sugar and press each ball into a 2-inch round. Bake at 350°F on the center rack for 10 and a half minutes, until the bottoms are light golden but the edges show almost no color. Cool on the sheets for 1 minute, then transfer to wire racks to cool completely.
04 -
Transfer the room-temperature frosting base to the bowl of a stand mixer. Beat with the paddle attachment on medium speed for 30 seconds until smooth. With the mixer on medium speed, add softened butter a tablespoon at a time. Scrape the bowl, then beat on high speed for 2 minutes until the frosting is fluffy and light.
05 -
Prepare a large piping bag fitted with an open star tip (1M). Pipe a rosette of frosting onto the top of each cooled cookie. Refrigerate for 30 minutes to set the frosting if desired. Press a halved candied cherry, rounded side up, into the center of each rosette.