Step 1: Make the Dough: In a medium bowl, whisk together flour, baking soda, salt, and spices. In a large bowl, cream butter and brown sugar until fluffy. Add egg, vanilla, and molasses. Beat until combined. Gradually add dry ingredients until dough forms. Divide dough in half, flatten into disks, wrap in plastic, and chill for 1–2 hours.
Step 2: Shape the Cookies: Preheat oven to 350°F (175°C). Roll out dough on a lightly floured surface to ¼-inch thickness. Use cookie cutters to cut out shapes. Place cookies on a parchment-lined baking sheet.
Step 3: Bake: Bake for 8–10 minutes until edges are firm but centers slightly soft. Cool cookies completely on a wire rack before decorating.
Step 4: Make Royal Icing: In a bowl, whisk egg whites (or meringue powder mixture) until foamy. Gradually add powdered sugar and lemon juice/vanilla. Beat until glossy and thick (about 5 minutes). Divide and color with food coloring if desired.
Step 5: Decorate: Transfer icing to piping bags with fine tips. Outline cookies, fill in with icing, and decorate with details. Allow icing to set completely before stacking or storing.