In a big mixing bowl or stand mixer, mix butter, oil, sugars, water and vanilla till clean.
Add eggs and blend till simply mixed.
In a medium mixing bowl, mix flour, salt, baking soda and cream of tartar.
Regularly mix dry substances into moist substances.
Refrigerate dough half-hour and preheat oven to 350°F.
On a parchment lined cookie sheet, drop massive (golf ball measurement) dough balls and press with a small greased glass to flatten and use the again of a spoon to make a pool for the icing.
Bake 8 minutes.
ICING
Cream butter, milk, sugars, vanilla and salt till creamy.
Utilizing a teaspoon, fill the baked sugar cookies.
