In a large bowl, whisk together all dry ingredients (flour through baking soda).
In a separate bowl, cream together the butter and brown sugar until smooth. Add the egg, molasses and vanilla and mix until thoroughly combined.
Gently stir the dry ingredients into the wet ingredients, mixing only until just combined.
Refrigerate the dough, tightly covered with plastic wrap, for at least one hour, or up to a few days.
Before you start forming the cookies, preheat oven to 350 degrees. Roll level tablespoons of dough into balls.
Pour granulated sugar into a bowl and coat each ball evenly with sugar before placing on an ungreased baking sheet.
Bake for 10 minutes, or until set around the edges, but still slightly soft in the middle. Let cookies cool for 5-10 minutes before transferring to a cooling rack