Step 1
Place racks in upper and lower thirds of oven; preheat to 375°. Whisk 2 cups (250 g) all-purpose flour, 1½ tsp. Diamond crystal or 1 tsp. Morton kosher salt, and ¾ tsp. baking powder in a medium bowl to combine.
Step 2
Whisk 1 large egg, 1 large egg yolk, 2½ tsp. vanilla extract, and ¼ tsp. almond extract in another medium bowl.
Step 3
Beat ¾ cup (1½ sticks) unsalted butter, room temperature, 1 cup (110 g) powdered sugar, and ¼ cup (50 g) granulated sugar in the bowl of a stand mixer fitted with the paddle attachment on medium speed until light and fluffy, about 4 minutes. With the motor running, gradually stream in egg mixture, scraping down sides of bowl as needed, until mixture is thick and homogenous, about 1 minute. Turn off mixer and add half of dry ingredients; mix on low speed just until dough starts to come together but is still slightly sandy, 30–60 seconds. Add remaining dry ingredients and mix until just incorporated, 30–60 seconds (be careful not to overmix).
Step 4
Scrape half of dough into pastry bag fitted with tip, press out excess air, and twist top to seal. Using moderate pressure, pipe dough into 2″ diameter swirls, if making sprinkle or maraschino cherry cookies, or 2″-long strips, if making sandwich cookies, onto a parchment-lined baking sheet, spacing at least 2″ apart. (If dough does not release from bag easily, use your finger or the tip of a butter knife to clip it off.) Refill bag and repeat with remaining dough on another parchment-lined baking sheet. Freeze cookies 10 minutes.
Step 5
Bake cookies, rotating baking sheets top to bottom and front to back halfway through, until golden underneath and just barely golden on top, 10–12 minutes. Let cool on baking sheets.
Step 6
To make sprinkle cookies, brush piped cookies with 1 large egg white and top with rainbow sprinkles before freezing. Continue as directed.
Step 7
To make maraschino cherry cookies, Drain one 12-oz. jar maraschino cherries and rub cherries between paper towels to remove excess juice. Let sit on fresh paper towels at room temperature while you make the dough. Using a ½ tsp. measuring spoon, make an indent in the middle of each piped cookie and freeze as directed. Place a cherry in each indent. Bake as directed, let cool, then dust cookies with powdered sugar. Dip a pastry brush or finger in water and brush or wipe sugar from cherries if desired.
Step 8
To make chocolate-dipped sandwich cookies, Spread 1 tsp. apricot preserves over bottoms of half of the baked cookies. Place cookies without preserves, bottom side down, on top to make sandwiches.
Step 9
Combine 12 oz. semisweet or bittersweet chocolate, coarsely chopped, and 1 Tbsp. refined coconut oil in a large microwave-safe bowl. Microwave on high in 30-second bursts, stirring after each, until melted and smooth. (Alternatively, heat chocolate and oil in a bowl set over a saucepan of simmer water, stirring occasionally, until melted and smooth; make sure bowl does not touch water. Remove bowl from heat.)
Step 10
Place rainbow sprinkles in a small bowl. Dip half of each cookie in melted chocolate to coat, then immediately dunk chocolate-coated halves in sprinkles. Place cookies on a wire rack and let sit at least 1 hour for chocolate coating to set up before serving.
Do Ahead: Cookies can be piped onto baking sheets 1 week ahead. Freeze until firm, then wrap tightly in plastic. Bake directly from frozen, adding about 2 minutes to baking time.