Preheat the oven to 325ºF and lightly grease a 10-inch oven-proof skillet (does not need to be cast-iron).
In a medium bowl, whisk together the almond flour, sweetener, collagen, baking soda and salt.
Add the melted butter, egg, and vanilla extract and stir until the dough tomes together. Stir in the chocolate chips, reserving a tablespoon or so for the top of the cookie.
Spread the dough in the prepared skillet and top with the remaining chocolate chips. Bake 20 to 25 minutes, until light golden brown. The cookie will be very soft and puffed when removed from oven (it won't seem cooked through).
Let cool at least 15 minutes before serving. When warm, it will not come out in proper pieces so you will need scoop it out to serve onto plates. It will continue to firm up as it cools so if you want to serve it in pieces, let it cool completely before cutting. I recommend it warm for extra gooey-ness!
Video
Notes
If you don't want to use collage, replace with another ¼ cup of almond flour.