For the cookies: Preheat oven to 350 degrees. In a mixing bowl whisk together flour, baking soda, salt and cream of tartar for 20 seconds, set aside.
In the bowl of an electric stand mixer fitted with the paddle attachment, cream together sugar and butter until combined.
Mix in egg, then mix in egg yolk and vanilla extract. With mixer set on low speed slowly add in dry ingredients and mix just until combined (dough with will thick, stop mixer and mix by hand to get flour at bottom if needed).
Scoop dough out 1 1/2 Tbsp (about 33g) at a time and shape into balls. Transfer to a baking sheet lined with parchment paper or a silicone liner, spacing cookies 2-inches apart.
Bake in preheated oven 10 - 12 minutes (cookies should appear slightly under-baked). Remove from oven and allow to rest several minutes then transfer to a wire rack to cool completely.
Repeat until all of the dough has been used up. Once cookies are cool (and just before serving) frost cookies with cream cheese frosting and top with fresh fruit.
For the frosting: In the bowl of an electric stand mixer fitted with the paddle attachment cream butter then blend in cream cheese and mix until smooth. Add powdered sugar and vanilla and mix until light and fluffy.
*If you don't want buy as many kinds of fruit as I did I'd recommend using diced strawberries, blueberries and diced kiwi.