In a bowl, add the passion fruit pulps and the oat flakes, mix until combined.
Transfer to a saucepan and add the water and the cinnamon stick, turn on the heat and stir until it starts to boil, cover the pan and let it all cook for 10 minutes.
After this indicated time, let the mixture cool down a bit and transfer it all to a blender. Blend very well for 1 minute.
After that, transfer the mixture to a bowl, by passing it through a sieve.
Then using a scoop, transfer half of this mixture to jar and set the other half aside.
Next, pour half of the mixture back in the blender, add the sugar and blend for 2 minutes.
Now, transfer this sweetened mixture back to the bowl filled with the other half, add the vanilla extract and mix.
Transfer it all to a jar and serve with some ice cubes.