Preheat your oven to 325°F. Line a 9-inch square baking pan with greased aluminum foil and set it aside.
Make the blondie layer.
In a large bowl, place the flour, xanthan gum, salt and baking soda, and whisk to combine well. Add the brown sugar, and mix to combine and break up any lumps in the brown sugar.
Create a well in the center of the dry ingredients, add the butter, eggs and egg white, and vanilla, and mix to combine. The batter will be very thick and relatively sticky.
Transfer about half of the batter to the prepared baking pan, and spread it into an even layer with a moistened knife or spatula. Place the pan in the center of the preheated oven, and bake for 10 minutes.
The crust should be mostly set. Remove from the oven and set aside to cool briefly while you make the cheesecake layer.
Reduce the oven temperature to 300°F, and place a pan filled with room temperature tap water on a rack in the bottom position in the oven.
Make the cheesecake layer.
In a large, clean bowl, place the cream cheese and beat until light and fluffy.
Add the granulated sugar, vanilla, and salt, and beat again until very well-combined. Add the egg, and beat again until just combined.
Add most of the chocolate chips, reserving a few to sprinkle on top, and fold into the cheesecake batter with a separate spatula until they’re evenly distributed throughout the batter.
Aseemble and bake.
Pour the cheesecake layer on top of the parbaked blondie layer in the baking pan, and spread into an even layer with a spatula.
Scoop the remaining blondie batter in dollops all around the top of the cheesecake layer.
Spread the blondie batter as evenly as you can over the top of the cheesecake batter. The layers will likely mix a bit, which is fine.
Sprinkle a few more mini chips on the very top.
Place the pan in the center or top of the 300°F oven (with the pan of water on the bottom) and bake for about 50 minutes or until the top appears set and doesn’t jiggle easily when shaken lightly from side to side. The top will not be completely firm to the touch.
Remove the pan from the oven and allow the blondies to cool completely in the pan. Once cool, remove the blondies from the pan and slice into 9 equal pieces with a sharp, wet knife.
Serve chilled or at room temperature. Wrap tightly and freeze any leftovers.