Using an electric mixer, cream together butter and sugar on medium-high speed until light and fluffy, about 3 minutes. Meanwhile, combine flour, baking powder, and salt in a separate bowl.
Reduce mixer speed to low and add the egg, vanilla, and almond extracts to the butter until combined. Lastly, add the dry ingredients and mix until just incorporated. Gather the dough into a disc and cover in plastic wrap. Refrigerate for 8 hours or preferably overnight.
Preheat oven to 325 degrees F. Place two baking sheets in the refrigerator to chill. Generously flour a smooth work surface and rolling pin, and have plenty of additional flour on hand.
Line one of the chilled baking sheets with parchment paper. Remove dough from the refrigerator and slice off a 2-inch knob. Rewrap the dough and store in the freezer. (You want the dough to be as cold as possible when rolling it.)
Working very quickly, roll out the dough to 1/8-inch (plus) thickness-too thin and the dough becomes unworkable, too thick and you can't tell what the cookie shapes are when baked. Be sure to keep flouring underneath the dough as well as on top, and use a bench cutter to prevent it from sticking to the surface. (I can't emphasize the importance of flour enough!)
Using well-floured 1 1/2-inch cookie cutters (holiday-themed or round), cut dough into desired shapes and place on baking sheet. (The best way to do this is to make sure the dough stays in the cutter, then gently push it out onto the pan. Removing the cut dough with a spatula directly from the work surface can cause it to stick or lose its shape.) Gather up the soft scraps into a small round and place in a bowl in the freezer. Repeat the above process until you have used up the original dough. Freeze the filled baking sheets until the cookies are firm, about 5 minutes. Bake the first pan of cookies until light golden brown and just a bit crisp, 12 to 13 minutes. Cool completely.
Wait until the scraps of dough in the freezer have firmed up, and continue cutting out the remaining cookies. Bake on the second chilled sheet pan, just like above. Repeat with all the scraps until all the dough is used.
Place a large cooling/wire rack over a baking sheet or parchment paper. When all the cookies have cooled, melt the almond bark according to package directions. Using your finger (or a small paint brush), spread a smooth coat of almond bark onto a cookie and clean up the edges with a thin cotton swab, such as a q-tip. Alternatively, cookies can be dunked in the almond bark and coated on each side. Place on wire rack to set. (Reheat almond bark in 15-second increments as necessary.)
Immediately sprinkle the iced cookie with nonpareils and set aside to harden. Cookies can be stored in an airtight container for up to 3 days.