Preheat oven to 170C (fan).
Wash the pumpkin, peel it and cube it, until you have 1 big full cup. Steam it for 15 min.
Using a small blender, blend your steamed pumpkin to have a smooth puree.
Put all the ingredients (pumpkin puree, rice flour, raw cacao powder, baking soda, salt, almond butter, maple syrup, vanilla) in a high speed blender and blend until smooth. You might need to scrap the sides once or twice and blend again.
If you don't have a good blender, using a medium bowl mix together (with a whisker) pumpkin puree, almond butter, maple syrup and vanilla. In another bowl mix rice flour, raw cacao powder, baking soda and salt. Then incorporate the dry ingredients to the wet ingredients and mix well until you have a smooth and well combined texture.
Line a rectangular cake pan (approx. 15cm x 24cm to have a high gooey brownie texture) with parchment paper.
Pour the mixture into the lined pan and smooth it evenly with the back of a spoon.
Bake on the center of the oven rack for 17-20 minutes. Take it out and remove the brownie from the cake pan (keeping the waxing paper around). Let it cool down (with the waxing paper) to firm up a little bit more.
Finally remove the waxing paper and serve it straight away or keep it in the fridge for 2-3 days.