In a large mixing bowl, combine cornstarch, cocoa powder, and salt. Add softened butter, brown sugar, and molasses. Beat until creamy, about 2-3 minutes.

Add eggs one at a time, blending well after each addition. Gradually mix in flour until a soft dough forms, about 1-2 minutes.

Wrap the dough in plastic wrap and refrigerate for at least 1 hour.

Roll out the dough to ¼-inch thickness and cut out cookies using a coffin-shaped cookie cutter. Place on parchment-lined baking sheets.

Bake in a preheated oven at 350°F (175°C) for 10-12 minutes until edges are firm.

Allow cookies to cool on the pan for 5 minutes, then transfer to wire racks to cool completely.

Make royal icing by beating confectioners' sugar, meringue powder, and vanilla until smooth. Tint with food coloring and decorate the cooled cookies.