In a large mixing bowl with a hand mixer or in a stand mixer with a paddle attachment, cream together the butter and sugar until light and fluffy.
Add the molasses and eggs (one at a time), mixing to combine.
In another bowl, whisk together the flour, cinnamon, ginger, allspice, baking soda, and salt.
With the mixer on low, slowly add the dry ingredients into the wet ingredients.
Once the dough starts to come together, turn it out onto a lightly floured surface and knead until well combined.
Divide the dough into two disks and wrap each with plastic wrap. Place any dough that you are not using in the refrigerator.
Preheat the oven to 375 F. On a lightly floured surface, roll out one portion of dough to 1/4 to 1/2 inch thickness.
You might need to add more flour if the dough is too sticky.
Cut out shapes and place on a parchment-lined baking sheet, making sure the cookies are 1 inch apart. Bake for 8-10 minutes.
Cool completely before removing cookies from the pan.
In a large mixing bowl with a hand mixer or in a stand mixer with a paddle attachment, beat the confectioners’ sugar, water, peppermint extract, and meringue powder until icing forms peaks (7-10 minutes at low speed with a heavy-duty mixer, 10-12 minutes at high speed with a hand-held mixer).
Note: For stiff icing (used for outlining), use 1 tablespoon less water. For the thinned (flood) royal icing add an additional teaspoon of water at a time until you reach a good consistency.