On low heat, melt butter in a saucepan. Mix in brown sugar until dissolved, then mix in molasses.
Remove from heat, and transfer to a mixing bowl. Let molasses mixture cool until luke warm, then whisk in egg.
Slowly whisk in flour, powder, soda and salt until a dough firms and all ingredients are thoroughly mixed.
Divide dough into 2 sections. Wrap both sections in cling wrap, place in refrigerator and let cool for at least 1 hour. You want the dough to be chilled, so that the dough isn't sticky.
Once thoroughly chilled, preheat oven to 350 degrees.
Place dough on a well-floured surface, and roll out so that the dough is 1/4 inch thick. You can make the cookies thicker or thinner, however thinner dough will make the cookies crispy.
Cut out shapes, and place on a parchment paper lined baking sheet. Bake for 8-10 minutes.