Cover a baking sheet with parchment paper. Lightly oil the paper with 1/2 teaspoon of liquid vegetable oil (coconut or peanut oil). This will prevent the cookies from sticking to the paper. Set aside.
In a food processor with the S blade attachment, add ripe avocado and sugar-free maple syrup (or liquid sweetener you like). Process for 30 seconds until it forms a creamy avocado batter with no lumps.
Stop, add egg, nut butter, and cocoa powder. Process again for 30 seconds. Scrape the bottom and side of the bowl and process for an extra 15 seconds to make sure all the batter is combined - no lumps.
Transfer the chocolate cookie batter onto a mixing bowl. It will bit moist and sticky. That is what you want. Stir in chocolate chips and vanilla - if used.
Combine with a spatula until the chocolate chips are evenly incorporated. Taste the batter and adjust with 2-3 drops of liquid stevia - only if you want a sweeter cookie. I did not add any to mine, and my kids love them, but if you have a sweet tooth, I recommend adding a few drops of stevia to make them sweeter. Add one drop at a time and see how it tastes.
Prepare a small bowl with warm water, dip a spoon in the water, and use that spoon to sample some chocolate cookie batter from your bowl. The water will prevent the batter from sticking to your spoon.
Spoon the chocolate batter onto the baking sheet - I used another spoon to push the batter out of the first spoon. Use a silicone spoon or spatula to flatten the cookie into a cookie shape. The batter won't stick onto silicone which makes it easier to spread.
Repeat until you form 6 jumbo cookies. Those cookies won't spread, so you don't need to leave more than half a thumb of space between each.
Sprinkle extra chocolate chips on top of each cookie if you like.
Bake for 12-15 minutes or until the center is set.
Cool it down for 5 minutes on the baking sheet, then transfer onto a cooling rack to cool down.
Store the cookies in the fridge for up to 5 days in an airtight container.
Low-carb/sugar-free: make sure you are using natural maple Flavored Sugar-Free Syrup and sugar-free chocolate chips.Vegan option: swap egg for a chia egg. Combine 1 tablespoon of chia seeds with 3 tablespoons of water. Sit for 15 minutes then use it as an egg in the cookie batter.Nut-free option: replace nut butter with sunflower seed butter here.Net carbs per cookies (carbs take away fiber): 5.5g