Beat butter and 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 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. (OR freeze for up to a month, just thaw on the counter or in the fridge.)
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. (If you're having ANY difficulty lifting them, slide the parchment onto a baking sheet and pop in the freezer for 10 minutes to firm up the dough.) Bake for 6-8 minutes, until 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 for a few minutes as needed anytime it gets too soft to work with.
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.