Beat butter and brown sugar on medium-high speed in standing mixer until light and fluffy, about two minutes, stopping to scrape down sides and bottom of mixer occasionally. Beat in molasses, and then eggs.
In a separate bowl, whisk together flour, baking soda, baking powder, baking soda, salt and spices.
Add flour mixture to mixer with speed on low; beat until combined. Divide dough into two equal piles on top of parchment or wax paper; flatten into disc shapes and wrap up in the paper. Refrigerate 1 hour, or up to 48 hours in advance.
Preheat oven to 375ºF. Working with one disc at a time, roll dough between sheets of floured parchment or wax paper to about 1/4" thick. Use a cookie cutter to cut out shapes, then lift them out with a metal spatula. Bake for about 8 minutes, or until just set and no longer shiny.
Press the dough scraps into another disc and repeat the process until all the dough is used. Transfer the dough to the freezer (see note in post) for a few minutes as needed if it gets too soft to work with.
Cool completely before decorating. Get the Royal Icing recipe I used here.
*I measured my flour by weight which I strongly recommend here, as 6 cups leaves a lot of room for variability - flour packs, and a little bit more or less in each "cup" can make a big difference in the final result.