Preheat the oven to 325°F. Lightly spray an 8-to-10-inch cast-iron skillet with cooking spray and set aside.
In a large bowl, whisk together the egg, cashew butter, coconut oil, maple syrup, nondairy milk, and vanilla until well combined. Add the almond flour, collagen peptides (if using), cinnamon, baking soda, and half the flaky salt. Gently fold the dry ingredients into the wet mixture, and stir until combined. Then gently stir in ½ cup of the chocolate.
Transfer the dough to the prepared skillet, and use a silicone spatula to smooth the top. Scatter the remaining 3 tablespoons of chocolate and the remaining flaky salt on top, and bake on the center rack of the oven for 18 to 20 minutes, or until a toothpick inserted in the center comes out clean. Switch the oven to broil on medium-low to turn the cookie a little more golden on top, 1 to 2 minutes. Watch carefully – the top can burn quickly!
Allow the cookie to cool slightly. Cut it into squares or wedges, or use a spoon to eat it right out of the skillet.
Serve with vanilla flavored coconut-milk ice cream (or your favorite flavor!) if you want even more dessert goodness. Enjoy!
Tip to make individual cookies: increase the amount of almond flour by ¼ cup, and use a cookie scoop to arrange portions of dough on a parchment-lined baking sheet. Bake for 8 to 10 minutes, or until golden brown.