In a large bowl or the bowl of a food processor, whisk together the all-purpose flour, the Redpath® Icing Sugar, and salt until thoroughly combined.
Add the butter and shortening to the dry ingredients. Using a pastry blender/cutter or hands (or if using a food processor, pulse several times), cut and work the fats into the flour mixture until mixture looks like coarse sand with pea-sized lumps of butter and shortening scattered throughout. The mixture should hold together when squeezed.
In a small bowl, whisk together egg, milk, and vanilla extract. Drizzle mixture over the flour-butter mixture. Stir or process just until combined.
Divide dough in half (approximately 300 g for each half). Shape each portion into a flat rectangle; wrap well in plastic wrap.
Place into the fridge to chill; at least 1 hour, or up to 2 days.
Remove dough from fridge about 15 minutes before rolling.
On a lightly floured work surface, or between parchment paper sheets, roll each portion of dough out to ⅛-inch thickness. Carefully place each portion of the rolled-out dough onto a large parchment-lined baking sheet.
With a 3½- to 4-inch ghost-shaped cookie cutter, cut out an equal number of ghosts from each portion of dough. Remove excess dough; dough scraps can be chilled again and rerolled if desired. Note that the resulting pastry may not be as flaky or tender as the once-rolled dough.
If dough is getting too soft or warm to work with, place the baking sheets of dough into the fridge to chill.