Combine the flour, sugar, baking powder, cinnamon, ginger, allspice, cloves, nutmeg, and salt in a large mixing bowl and whisk together.
Add the grated frozen butter, toss in the flour mixture, and then use your hands to break up the butter into pea size pieces.
Make a well in the center of the dry ingredients, and in the well, add the sourdough starter, egg and egg yolk, vanilla, molasses, and milk. Mix the wet ingredients together and then stir them in with the dry ingredients until just combined, avoiding overmixing.
Shape the scone dough into an 8-inch round disk. Cut it into eight equal pie-shaped pieces, place on a parchment-lined baking sheet.
Cover the scones (with plastic wrap or something air-tight) and allow to ferment in the refrigerator for 8-72 hours.
When ready to bake, preheat the oven to 425 degrees Fahrenheit. Remove the baking sheet from the refrigerator, uncover the scones, and bake for 17-20 minutes, or until lightly golden on the tops and edges. Remove and allow to cool to room temperature.
Meanwhile, combine the softened cream cheese and butter and mix with a hand mixer until creamy. Add the powdered sugar, salt, vanilla, and milk and mix until smooth and creamy. Put cream cheese mixture into a piping bag (or a plastic storage bag with the corner clipped) and top the scones. Enjoy!