For the shortbread: Heat the oven to 325 degrees F. Spray the sides and bottom of 9-inch springform pan with cooking spray.
In the bowl of a food processor, combine the flour, sugar, milk powder, nutmeg, ginger, cinnamon and salt, keeping the butter cold up until the last minute. Pulse several times to mix the dry ingredients, then add the cold butter. Pulse several times (10 to 12) or until the butter is in uniformly pea-size pieces. Do not overprocess; the mix is dry and will not come together.
Remove the bowl from the processor. Dump the contents directly into the springform pan and spread evenly. (This shortbread leans more toward a traditional drier, more crumbly Scottish shortbread.) Press down the shortbread with the bottom of a flat measuring cup to compress the dough. Score the shortbread into 16 wedges.
Place the pan in the heated oven on the center rack. Set your timer for 20 minutes. Rotate the pan, reset the timer for an additional 20 minutes.
Check the shortbread after 40 minutes (total). They should be lightly brown in color and slightly firm to the touch. You may need to add a few minutes, depending on your oven.
Remove the pan from the oven, let cool for 5 minutes before releasing the pan. Once the sides are removed, carefully cut the cookies, following the pre-scored lines.
Once cut, allow the cookies to cool completely before glazing.
For the bourbon glaze: In a small heat-proof bowl, sprinkle the gelatin over 3 tablespoons water; set aside to bloom for 5 minutes.
Bring a small saucepan of water to a simmer.
Place the bowl with the bloomed gelatin over the simmering (not boiling) water. You want it to melt completely.
Remove the bowl from the double boiler and add the confectioners' sugar, bourbon, maple syrup, vanilla seeds and bean and salt. Mix thoroughly and then remove the vanilla bean.
Glaze the shortbread: A wire cooling rack will help with this step. I take a shortbread wedge and turn it over, dipping the top of the wedge in the glaze. Allow the excess glaze to drip back into the bowl, the place the shortbread, glazed side up, on the rack. Continue until all the shortbread are glazed. Allow to air dry, remove from the rack and store in an airtight, odor-free container at room temperature. These are best eaten within 2 to 3 days.
NotesThis recipe will yield more glaze than you will need for the shortbread. Store the leftover glaze at room temperature and use it on waffles, pancakes, cupcakes, or doughnuts. It's too good not to have around.