Preheat your oven to 350°F (175°C). Line a 9-inch square baking pan with parchment paper and set aside.

Cut the avocados in half, remove the pits, and scoop the flesh into a bowl. Mash them thoroughly until smooth, ensuring no large chunks remain.

In a large mixing bowl, whisk together almond flour, cocoa powder, baking soda, and salt until well combined.

In another bowl, mix the mashed avocados, maple syrup, eggs, and vanilla extract until smooth and well combined.

Gradually add the dry ingredients to the wet ingredients, stirring until just combined. Be careful not to overmix.

Fold in chopped walnuts and dark chocolate chips if using, ensuring they are evenly distributed throughout the batter.

Transfer the batter to the prepared baking pan and spread it evenly with a spatula.

Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted into the center comes out mostly clean with a few moist crumbs.

Allow the brownies to cool in the pan for 10 minutes before transferring to a wire rack to cool completely. Slice into squares and serve.

Keep the brownies in an airtight container at room temperature for up to 3 days, or refrigerate for up to a week.

Wrap individual brownies in plastic wrap and store in a freezer-safe bag for up to 3 months. Thaw at room temperature before serving.