On the stove top, using a small pot, melt 10 tablespoons of the butter (cut into small pieces) over medium heat. Whisk continually until the butter melts. Pour into a bowl and add in the remaining 4 tablespoons of unmelted butter. Set aside.
In a large bowl, whisk together 1/4 cup of dark brown sugar, granulated sugar, flour, baking powder and baking soda. Set aside.
Get the bowl of butter that was set aside earlier. Add the remaining dark brown sugar and salt to the butter and whisk until creamy. Next, whisk in the egg yolk, egg and vanilla.
Put the egg and butter mixture into the bowl of dry ingredients. Stir until dough forms.
Roll dough out with a rolling pin, to 1/2-inch thickness. Use a cookie or biscuit cutter and cut out shapes and place on parchment lined baking sheets. Sprinkle generously with sugar crystals.
Bake in preheated 350F oven for 8-12 minutes or until lightly browned. Leave on baking sheet for a couple of minutes and then transfer to cooling rack.