In a bowl, whisk together all of your dry ingredients including; almond flour, coconut flour, xanthan gum, baking soda, baking powder and salt. Set aside.
Heat a 12-inch cast iron skillet over medium heat. Add the butter in chunks and occasionally stir it until it's melted.
Continue to heat the butter, stirring often until it begins to simmer and eventually gets very foamy and white on top (~5-6min). Continue to stir just until you see it turn a golden brown colour, then immediately (gently) remove it from the heat.
Give it a few more occasional stirs, then let your browned butter cool to ~room temperature (where it's still melted but not hot to the touch) before adding the rest of your ingredients.
During this time you can also pre-heat your oven to 330*F.
Once your butter has cooled, add the sweeteners and eggs along with the vanilla extract. Whisk everything together using a rubber whisk until it's smooth.
Then add half of your flour mixture from before and stir it until it's completely blended with the wet ingredients.
Add the second half of the flour mixture and stir again, very well, until your batter becomes quite thick.
Add the chocolate chips and gently stir them in.
Then press your cookie batter evenly into the bottom of the skillet, smoothing out the sides and top.
Bake your skillet cookie for ~20min (on a high oven wrack if your oven heats more-so from the bottom up).
Let the cookie cool for a bit before slicing and serving with some low carb ice cream! Enjoy your Keto Chocolate Chip Skillet Cookie!