Cream Butter, Vanilla, Salt and Sugar together in the bowl of a stand mixer. Whip until light in color and fluffy. Scrape down the sides and bottom of the bowl and add the eggs. Whip again until fully incorporated. Dissolve the baking soda in the milk and set aside. Add four cups of flour and mix until incorporated. Add the milk mixture until incorporated. Add the rest of the flour (adding the last cup slowly, and as needed) until the dough starts to pull away from the sides of the bowl. It should essentially clean the sides of the bowl. Dough should be soft and not sticky.
Divide dough into 3 separate sections. Roll each section out in between two pieces of waxed paper using guide rulers or an adjustable rolling pin. I usually roll my dough to 3/8” thickness. Place dough onto a baking sheet and cover. Place into the fridge for at least 1 hour to chill.
Cut to desired shapes, place on baking sheet, and bake at 350°. Depending on the size and thickness of your shapes, dough might need to cook for 6-18 minutes. Cookie is thoroughly baked through when the surface is no longer shiny and the edges cannot be indented with your finger.
When you remove the cookie sheet from the oven take a fondant smoother or use the bottom of a smooth spatula to gently flatten any air bubbles. Let cookies rest on pan for 5 minutes and then remove to a cooling rack to cool completely.