Preheat your oven to 350°F (175°C). This ensures that the skillet cookie bakes evenly and thoroughly.

Place your cast iron skillet on the stove over low heat. This will help to melt the butter evenly when added.

In a mixing bowl, combine the almond flour, erythritol, cocoa powder, baking soda, and salt. Whisk together until well combined. This step is important to avoid clumps and ensure even sweetness.

In another bowl, mix the melted butter, egg, and vanilla extract. Whisk until fully combined. The melted butter should be cool enough not to cook the egg.

Pour the wet ingredients into the dry ingredients. Stir with a spatula until just combined. Be careful not to overmix, as this can make the cookie tough.

If using, fold in the sugar-free chocolate chips for extra flavor and texture.

Pour the cookie dough into the preheated skillet, spreading it evenly. This ensures that it bakes uniformly.

Transfer the skillet to the oven and bake for 15-20 minutes, or until the edges are set and the center is slightly soft. The cookie will continue to firm up as it cools.

Remove the skillet from the oven and let it cool for about 10 minutes. This allows the cookie to set properly.

Slice into wedges and serve warm, optionally with a dollop of whipped cream or a scoop of keto-friendly ice cream.