Puzzle-shaped cookie cutters or paring knife or pizza cutter
Pastry bag with round tip or plastic sandwich bag
1 pound confectioners' sugar
5 Tbsp. meringue powder
Scant 1/2 cup water
Mix together flour, baking soda, and baking powder in a medium bowl. Set aside.
Mix butter and sugar with an electric mixer on medium speed until fluffy, about 2 minutes; mix in spices and salt. Mix in egg and molasses, occasionally scraping down sides of bowl. Add flour mixture; mix on low speed until combined. Divide dough in half; pat into two disks. Wrap in plastic wrap; refrigerate 1 hour.
Preheat oven to 350 degrees. On a lightly floured surface, roll out dough to about 1/8-1/4 inch thick.
If using puzzle-shaped cookie cutters, cut out as many as you desire. If you do not have the cookie cutters, cut rolled dough into six rectangles. Transfer to a parchment-lined baking sheet; refrigerate until firm, 20 to 30 minutes. Bake until cookies are set and edges are just starting to brown, 10 to 12 minutes. While cookies are hot, use a pizza cutter or paring knife to cut out desired puzzle shapes. Carefully lift edges of parchment to keep puzzle pieces together; transfer to a wire rack. Let cool completely.
For icing: Beat ingredients in a mixer bowl on low speed until smooth, about 7 minutes. If icing is too thick, add more water; if too thin, beat 2 to 3 minutes more.* Tint desired color with food coloring.
Fit a pastry bag with a 5/16-inch plain round tip; fill with 1/2 cup royal icing. Tie end with a rubber band.
Outline each puzzle piece with tinted icing; fill outlined area with more icing, smoothing with an offset spatula to make a thin layer.
*Don't add all the water at first; test on parchment with the stencil to determine the best consistency.