In a large mixing bowl, cream together the shortening and granulated sugar for 2-3 minutes until light and fluffy. Add the eggs and milk and mix to combine.
Place the flour, baking powder, and salt in a separate mixing bowl. Whisk until fully incorporated.
Add the dry ingredients to the wet mixture a little at a time, mixing between additions. Mix just until the dough is formed. Finally, mix in the vanilla extract.
Chill the dough for at least 1 hour before rolling it out. When rolling out the dough, cover your surface with flour to keep your dough from sticking. With a rolling pin, roll out the dough (about ½ inch thick) and cut out the cookies.
Preheat oven to 325°F and line a cookie sheet with parchment paper. Place cookies on the lined baking sheet and bake for 12 minutes or until the edges are slightly golden brown. Let them cool completely (10-15 minutes) before frosting.
FOR THE FROSTING
In a large mixing bowl, cream together the butter and shortening until light and fluffy (2-3 minutes). Add the powdered sugar one cup at a time, mixing between additions. Mix in the vanilla extract.
Add in the milk or heavy cream as needed. Add food coloring if desired. Frost your sugar cookies and enjoy!