• Preheat your oven to 350 degrees F.
• Line a 9x13 inch baking pan with parchment paper and be sure to leave a 2-inch overhang. (I did not use parchment paper and my bars turned out fine; but, I did generously grease my pan.)

Make the soft cookie base

• In a large bowl, whisk together the flour, cream of tartar, baking soda, and salt and set aside. In the bowl of a stand mixer fitted with a paddle attachment or a large bowl if using a hand-held mixer, cream the butter and sugar on medium speed until light and fluffy, about 2-3 minutes.
• Add the egg to the butter and sugar mixer and mix until just incorporated. Turn the mixer to low and add half the flour mixture, then half of the milk. Add the remaining flour mixture, then the milk and mix just until combined. Using a knife or offset spatula, evenly spread the cookie base batter into the bottom of the prepared baking pan.

Make the gooey layer

• In a small bowl, mix together the honey (or corn syrup), heavy cream and vanilla and set aside.
• In the clean bowl of a stand mixer fitted with the paddle attachment or a large bowl if using a hand-held mixer, cream the butter and sugar on medium speed until light and fluffy, about 2-3 minutes.
• Add the egg and let it fully incorporate into the mixture. Then sprinkle in the salt. Add the flour in three separate additions, alternating with the milk/honey mixture, starting and ending with the flour. Using an offset spatula or knife, evenly distribute and spread the batter over the cookie base.

Make the topping

• In a small bowl, whisk together the sugar and ground cinnamon. Sprinkle this evenly over the gooey layer.
• Bake in your preheated oven for about 25-30 minutes or until the top is golden brown. The gooey layer will eventually set once the bars have completely cooled.
• Remove the bars from the oven, let it completely cool, and then slice.