Whisk together the flour, yeast, sugar, salt, and baking powder., Add the shortening, mixing until evenly crumbly., Add the butter, mixing until roughly combined. Pea-sized bits of butter can remain., Add the milk, mixing until just combined. The dough will be quite wet., Transfer the dough to a well-floured work surface, and quickly and gently pat it into a 7" diameter, 1"-thick circle., Use a 2" round biscuit cutter to cut 9 biscuits. Pat together the scraps, and cut as many additional biscuits as you can. Place them close together on a lightly floured or parchment-lined tray or baking sheet. Cover with lightly greased plastic wrap or the cover of your choice, and allow the biscuits to rest at room temperature for 1 hour., After an hour, cover the biscuits with plastic wrap, and place the pan in the freezer for at least 1 hour. Overnight is fine. Alternatively, biscuits can be frozen up to 2 months., When ready to bake, preheat the oven to 400°F., Remove the biscuits from the freezer, remove the plastic, and space them on a lightly greased or parchment-lined baking sheet., Bake the biscuits for 16 to 18 minutes, until they're golden brown., Remove from the oven, and brush with melted butter, if desired.