¼cupheavy creamcan substitute half and half, whole, 2% or skim
Preheat oven to 350°F. Grease baking dish or pan.
In a large mixing bowl, combine butter, oil, sugars and vanilla until smooth. Blend in eggs.
Gradually add flour, salt, cream of tartar and baking soda until well incorporated.
Press dough into a greased pan.
Bake 20 minutes*. Allow to cool.
In a medium mixing bowl, combine butter, powdered sugar and milk until smooth.
Spread frosting over completely cooled cookie cake.
Substitutions and Variations
Butter - Omit salt in the recipe if using salted butter.Extract - Use your favorite! Almond extract also offers great flavor! Orange or lemon also taste amazing!Cream - Heavy cream creates a luxurious consistency, but you can use half and half or milk if needed.Sprinkles - You can add your favorite sprinkles to top the frosting and in the cookie base to mix this cake up for birthdays, holidays and more!
Baking time will vary depending on the pan you use. Reduce baking time for thinner cookie cakes checking in at 15 minutes and increase for thicker cakes if you want them more done.
How to Store
At Room Temperature - Store covered or in an airtight container up to 2 days at room temperature.
Refrigerate - Store in an airtight container up to 5 days.
Freeze - Freeze without frosting wrapped with plastic wrap and in an airtight container for up to 3 months. Bring to room temperature and frost.