Oven Prep & Pan Heating : Position a rack in the center of your oven and preheat to 350∘F (175∘C). Place the butter into your 8-inch oven-safe pan and set it over low heat on the stovetop. Allow the butter to melt completely, swirling the pan occasionally.
Creating the Liquid Base : Remove the pan from the heat and let it cool for 3-4 minutes; the handle should be warm, not hot. This prevents the egg from scrambling. Whisk in the golden erythritol blend until smooth. Add the room-temperature egg, vanilla extract, and almond extract, whisking vigorously until the mixture is glossy and emulsified.
Combining the Dry Mix : Add the almond flour, collagen peptides, baking soda, sea salt, and optional espresso powder directly into the pan. Switch to a flexible spatula and stir until the dry ingredients are just incorporated and no flour streaks remain. Do not overmix.
Forming the Cookie Dough : Reserve about 2 tablespoons of the chocolate chunks for the topping. Fold the remaining chocolate into the dough in the pan. Gently spread the dough with the spatula so it forms an even layer across the bottom of the pan.
Skillet Baking : Scatter the reserved chocolate chunks over the surface of the dough. Transfer the pan to the preheated oven. Bake for 18–20 minutes, or until the edges are a rich golden-brown and the center appears just set. The cookie will look slightly underdone and puffy, which is perfect.
Cooling and Setting : Carefully remove the pan from the oven and place it on a wire rack. Let the cookie cool in the pan for at least 20 minutes. This step is essential for the cookie to set and develop its gooey texture. Serve warm by scooping directly from the pan.
