Cream together the butter and sugar then beat in the eggs one at a time. Stir in the melted chocolate.
Add the flour, 1/2 cup at a time, beating well after each addition. Add the baking powder, soda, salt and cinnamon with the first 1/2 cup of flour.
Wrap the dough in waxed paper or plastic wrap and chill for at least an hour or overnight.
Preheat oven to 400 degrees Fahrenheit. Roll out the dough (you'll probably need to roll it out in batches, say 1/3 at a time) on a floured surface to 1/8" thickness and cut out with cookie cutters. Decorate with sprinkles.
Bake 5 to 8 minutes on a baking sheet lined with a silicone baking sheet or parchment. When the cookies just start to brown around the edges, they're ready. Let them cool on a wire rack.