Preheat oven to 350F and line a 9x9 square baking dish with parchment paper (for easy lifting). 

In a blender, place the chopped spinach, blueberries, and 2 teaspoons of water. Blend until a smooth puree form. Add a little more water if needed, you want the mixture to have the consistency of apple sauce, about 1 cup.

In a large bowl, combine the flour, sugar, cocoa powder, baking soda, and salt. 

Melt the butter and chocolate chips in a heat-safe bowl with the double boiler method by placing water in a small saucepot, placing the bowl on top with the butter and chocolate, and using the heat/steam to melt the chocolate. Once the chocolate chips have melted, turn off the heat and place the bowl on the counter. You can also melt them in the microwave, very carefully to not burn the chocolate, about 1 minute, stirring throughout. 

Pour the blended spinach and blueberry mixture into the melted chocolate bowl along with the vanilla. Stir to combine.

Pour the chocolate bowl mixture into the flour bowl. Add the eggs, and with a fork, mix everything until combined. 

Pour the brownie batter into the prepared pan. Bake in the preheated oven for 40 minutes, until the middles are done and no longer wet to the touch.

Remove from oven, allow brownies to cool down before slicing.