Preheat the oven to 325ºF and line a 9-inch square baking dish with parchment paper. (I like to grease the pan first, so the parchment paper will stay in place.)
You can make these brownies in a single bowl, mashing the avocado with a fork until relatively smooth, or you can make them in a food processor to get rid of all the avocado chunks. (I prefer using a food processor, but I've had good results with both methods.)
In a food processor, combine the avocado (peel and pit removed), cacao powder, eggs, coconut sugar, almond butter, baking powder, vanilla, and salt. Process until smooth, stopping to scrape down the bowl as needed.
Fold in the chocolate chips, then pour the batter into the prepared pan. (Decorate the top with a few extra chocolate chips, if desired.) Bake at 325ºF for 45 minutes, or until the center of the brownies looks cooked-through. (You don't want any jiggle when you shake the pan.)
Allow the brownies to cool completely. The avocado flavor is MUCH more pronounced if you try these warm, so please don't be tempted to taste them until they have come to room temperature. You can place them in the fridge if you want to speed up the cooling process, or you'll have to wait at least 2 hours for them to cool on the counter.
Slice the brownies into small squares and serve. It's normal for this brownie to stick to the knife a bit with you cut them, since they are flourless and very fudgy. Leftovers can be stored on the counter for up to 48 hours, or in the fridge in an airtight container for up to a week.