Beat butter, sugar, and molasses in a stand mixer until smooth. Mix in the egg, then add vinegar, baking soda, salt, and spices. Combine well.

Gradually mix in flour, 1 cup at a time, until the dough forms. Divide into two halves.

Roll out each dough portion between parchment sheets to ¼ inch thickness. Chill in the refrigerator for at least 1 hour.

Preheat oven to 375°F. Use cookie cutters to cut shapes from the dough. Chill cutouts for 10 minutes.

Bake for 8 to 12 minutes until edges are set. Cool completely before decorating.

Prepare royal icing by beating meringue powder, powdered sugar, vanilla, and water until stiff peaks form. Decorate cooled cookies.