Preheat the oven to 315°F/157°C. Line 3 cookie sheets with baking parchment.
In a medium bowl, whisk together the dry ingredients. Set aside.
Put the melted butter in a large bowl. Add the 2 sugars, and beat them in with a spatula. Then beat in the vanilla, molasses, egg yolk, and milk.
Add the dry mixture to the wet mixture, and stir until a stiff dough develops.
Form the dough into 1-inch-diameter balls (a 1-inch-diameter cookie scoop is helpful here), and toss them, 6 or 7 at a time, into the bag of sugar. Shake the bag to coat. Then arrange the balls 2 inches apart on the baking sheets.
FREEZER NOTE: If you are not going to bake all of your cookies at once, you can freeze them on cookie sheets. When the balls of dough are solidly frozen, transfer them to a zip-lock bag. Bake the balls at your leisure!
Bake in the preheated oven until the balls of dough flatten out, and their edges turn crisp -- about 18 minutes. For cookies that are crisp throughout, bake for about 20 minutes. Cool completely on wire racks. The cookies will continue to crisp as they approach room-temperature.