Preheat your oven to 180°C (350°F). Line a 12-cup muffin pan with liners.
Preparing the avocado muffins:
Add the wet ingredients to a large mixing bowl and blend using a stick blender. If you don't have a stick blender, add all the ingredients to a food processor or blender and blend until smooth. Then transfer the mixture to a large bowl.
Add the dry ingredients to the bowl and mix until just before it's combined and there are still some small pockets of flour.
Add the chocolate chips to the bowl and fold until just combined.
Use an ice cream scoop or a large spoon to divide the batter into your muffin pan (note 3). The batter should be thick enough for you to create a 'heaped mound' in each muffin cup (see reference images above).
If desired, sprinkle additional chocolate chips and chopped pistachios on top of the muffins.
Baking and storing the muffins:
Bake the muffins for 20-25 minutes or until you can insert a toothpick in a muffin and it comes out mostly clean. Avoid overbaking the muffins as it'll make them dry. These muffins are very moist so a few crumbs are fine.
Allow the muffins to cool in the muffin pan for 10 minutes (or until they aren't too hot). Remove the muffins and allow them to completely cool on a wire rack.
Enjoy the muffins warm or at room temperature. They're perfect by themselves or with some vegan butter or more avocado!
Store leftover muffins in an airtight container at room temperature for up to 3 days, in the fridge for up to 3 days or in the freezer for up to 1 month.
Notes
I recommend weighing the avocados as too much avocado will make your muffins heavy. Also, make sure you use a variety of avocado that doesn't turn bitter when baked. Some varieties will turn noticeably bitter when heated.
It's important to measure the flour accurately, otherwise your muffins will be dry and dense. If you're using measuring cups, use the spoon and level method where you fluff up the flour in the bag, use a spoon to add flour to a measuring cup, then level it off with a knife. If you scoop flour out of the bag with a measuring cup, it will pack too much flour into the cup and result in dry and dense muffins. Alternatively, use the grams measurements.
For the highest muffin tops, I recommend baking 6 muffins at a time in a 12-cup muffin tray. Spacing apart the muffins allows the hot oven air to bake them faster, resulting in higher tops. This means you'll need to bake the muffins in 2 lots.