- Pre-heat oven to 375°F and line a few baking sheets with parchment paper. (I bake them at 350°F in a convection oven) 
- In a large bowl, whisk together the flour, baking soda, and cream of tartar. Set aside. 
- In the bowl of a stand mixer fitted with the paddle attachment, cream together the butter, oil, and sugars on medium-high speed until light and fluffy, scraping the sides as necessary. 
- Reduce speed to medium and add the eggs, one at a time, mixing just until combined. 
- Add the vanilla and mix until combined. 
- Reduce speed to low and add the flour in three additions, scraping down the sides as necessary. 
- In a medium bowl, beat cream cheese until smooth. Add in the brown sugar. Beat on high until the brown sugar granules break down and it is a smooth consistency. Add chocolate chips and stir by hand. 
- Scoop out 1/4 cup of the sugar cookie dough for each cookie, dividing each in half. 
- Flatten the bottom half of the cookie in your hand, then put a teaspoon or two of the cream cheese filling in the center. (You can fill them with up to a tablespoon of filling, just make sure the edges of the cookie dough can seal.) 
- Place the top half of the dough over the filling, sealing the edges. Be sure to shape each cookie like a hockey puck so the edges do not burn. 
- Bake for 15-17 minutes. 
- Let cool on baking sheet.