Begin by preparing the cookie dough. In a large bowl, sift together the flour, baking soda, and salt. Set aside.
In a stand mixer with the paddle attachment, cream together the vegetable shortening, sugar, eggs, and vanilla. Once combined, add half of the dry ingredients. Begin to mix and pour in the buttermilk. Then add the remaining dry ingredients and mix until just combined. Refrigerate the dough for at least four hours or overnight.
After your dough has chilled, preheat your oven to 375 degrees F.
On a well-floured surface, roll out about a quarter of the dough to a 1/8 - 1/4-inch thickness, depending on your preference. Cut out the dough using a sweater-shaped cookie cutter. Transfer each cut out to an ungreased cookie sheet. Bake 8-10 minutes or until the first sign of browning appears on the surface of the cookies. Remove from the oven and transfer the cookies to a cutting board or your counter top to cool completely.
While the cookies cool, prepare your frosting*. With a mixer, cream together the vegetable shorting and butter. Slowly add the confectioner's sugar, one cup at a time. Mix in the vanilla extract. Add milk as needed for a smoother consistency. Divide the frosting into smaller bowls and add gel food coloring to achieve the desired colors.
Place the frosting in a piping bag with the desired tip. A small star tip is great for the sweater texture, and a round tip is recommended for details and dots.
Once your cookies have cooled, use the prepared piping bags to create designs on your sweater cookies.
Allow the frosting to set before packing and storing the cookies in an airtight container.
Notes
*I like to use a variety of colors when creating these cookies, so I double this recipe. Typically that will leave me with extra frosting, but I'd rather have extra in order to have fun with my designs without fear of running out.