Preheat oven to 350°F. Line two baking sheets with silicone liners, or mist the sheets lightly with cooking spray. Set aside.

In a large bowl, combine the cake mix, eggs, and oil with a spoon until a soft dough has formed. Drop rounded Tablespoonfuls of dough onto the prepared baking sheets, keeping about 2” between each dough ball. Using a flat-bottomed glass, dip the glass in sugar and gently press down onto each cookie to flatten it.

Bake for approximately 8-10 minutes, rotating pans halfway through baking time to ensure even cooking. Remove the pans from the oven and allow cookies to set for about 10 minutes before carefully transferring to wire racks to cool completely.

While cookies cool, make your cookie dough filling. In the bowl of a stand mixer, cream together the butter, brown sugar and white sugar until creamy, about 2 minutes. Add in the vanilla and milk. Lastly, add in the flour and salt. Stir in the chocolate chips by hand.

Flip over a cookie so it’s flat-side up. Top with a Tablespoon or so of cookie dough, then gently sandwich it with another cookie. Smooth out the sides of the filling if needed. Serve immediately, or store cookies airtight in the fridge, for up to 2 days.