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.