In the bowl of a stand mixer fitted with the paddle attachment, or in a large mixing bowl with hand beaters, beat butter on medium speed for 30-60 seconds, or until smooth. Add the sugar, vanilla, and orange zest; beat on medium speed until combined.
Add flour, cornstarch, and salt and beat until combined. Place the dough onto a sheet of plastic wrap and form into a round, flat disk. Wrap up the dough and chill in the refrigerator for at least 1 hour.
After an hour remove the dough from the refrigerator, and line two cookie sheets with parchment and set aside.
Lightly flour your counter and roll the dough out to ¼ inch thickness. Use a 2-inch round cookie cutter to cut the dough and place cut dough on the prepared cookie sheets. Chill the cookie sheets in the refrigerator for 30 minutes.
Preheat the oven to 325 degrees F while the cookie sheets are chilling. At the end of the 30 minute chill time, pop the cookie sheets into the oven and bake 14-16 minutes or until the cookies start to turn a pale golden color around the edges.
Cool for 5 minutes on the cookie sheet, then transfer to a wire rack to cool completely before icing.
FOR THE ICING:
In the bowl of a stand mixer fitted with the paddle attachment, or in a medium mixing bowl with hand beaters, beat butter until smooth and fluffy, about 3 minutes. Add the cranberry jam and mix until combined, about 30-60 seconds.
Add the sugar and pulse until combined, then beat on medium until light and fluffy, about 3-4 minutes. Add the milk, 1 teaspoon at a time, until the desired consistency is reached.
Transfer the icing to piping bag fitted with a 1M tip and frost cookies. Garnish with a sugared cranberry (optional).