Combine butter with sugar and beat on medium speed until well creamed together.
Add the egg, and vanilla extract. Mix into butter and sugar until egg is well beaten.
In a separate bowl, combine flour, baking soda and cream of tartar. Slowly add the dry ingredients into the batter and beat on medium low speed until well combined and dough forms. Add the sprinkles last and continue beating until the sprinkles are incorporated.
Refrigerate dough for a minimum of 30 minutes and up to 1 hour.
Preheat the oven to 350°F
Roll out the cookie dough onto a lightly floured surface. It’s helpful to use parchment paper on the top and bottom so the dough does not stick. Roll the dough into a circle until it’s about a ¼” thick.
Bake at 350°F for 15 to 18 minutes until the edges just start to turn golden brown. The center will still be a little bit soft but that’s okay.
Allow the cookie to cool completely.
For the frosting: allow the butter to come to room temperature so it is soft but not melted. Beat butter in mixer on medium speed until smooth and creamy.
Add the marshmallow creme and containing mixing for another 2 minutes.
Slowly add powdered sugar 1 cup at a time while continuing to beat on medium speed and then add the heavy whipping cream and clear vanilla extract. Beat until all ingredients are well combined.
Spread the frosting over the cookie, leave about 1-inch around the outside edge. You may have a little leftover frosting.
Top the pizza with sprinkles and strawberries and your toppings of choice. If you choose to add berries, you should add just before serving and they should be completely dry. I also had some leftover cookies, which I sprinkled on top.