Whisk flour, baking powder, and salt together in a medium bowl. Set aside.

In a large bowl, beat butter and sugar with an electric mixer on medium speed until light and fluffy, about 2 minutes. Scrape down the bowl.

Add egg, vanilla, and almond extract. Beat on low until combined, about 30 seconds.

Gradually add the flour mixture, mixing on low just until no dry streaks remain. Do not overmix.

Divide dough in half, flatten each into a disk, wrap in plastic, and refrigerate for at least 1 hour (or up to 2 days). Chilling prevents spread.

Preheat oven to 350°F. Line two baking sheets with parchment paper.

On a lightly floured surface, roll one disk to 1/4-inch thickness. Cut rounds with a 3-inch cutter. Use a sharp knife to cut each round into a half-circle (like a watermelon slice). Place 1 inch apart on prepared sheets.

Bake 8–10 minutes, until edges are just set and bottoms are lightly golden. The tops should not brown. Cool on the sheet for 5 minutes, then transfer to a wire rack to cool completely.

For the icing: In a medium bowl, whisk powdered sugar and meringue powder. Add water and beat with an electric mixer on medium-high for 4 minutes, until stiff peaks form. The icing should hold a sharp line when you lift the beater.

Divide icing into two bowls. Tint one portion red (use gel color — start with a tiny dab on a toothpick) and the other green. Cover both with damp paper towels to prevent drying.

Thin the red icing: add water 1/2 teaspoon at a time, stirring gently, until it flows like honey and a ribbon settles back into the bowl in 10 seconds. Keep the green icing thick.

Fit a piping bag with a small round tip. Fill with green icing. Pipe a thin green line along the curved edge of each cookie (the rind). Let set for 10 minutes.

Using a small offset spatula or the back of a spoon, spread red icing over the rest of the cookie, letting it flow right up to the green edge. Work one cookie at a time.

While the red icing is still wet, sprinkle black sanding sugar over the red area to look like seeds. Gently press the sugar into the icing. Let cookies dry uncovered at room temperature for 4 hours or overnight until the icing is firm to the touch.