Mix flours, flax meal, baking soda, sugar and vanilla seeds well
In the other bowl mash banana add raspberries and add milk, whisk so it comes together( few lumps of banana and raspberries are ok) Or you can use hand blender to make it completely smooth if you wish.
Pour wet ingredients over dry and let it sit while oven preheating to 180 degrees
When ready to bake line your mold with a baking parchment and slice rhubarb on the way that it fits and covers the bottom of the molds completely. Add whole raspberries alongside with Apple cider vinegar and just stir to combine.
Straight away pour it over rhubarb and bake for 35 minutes or till golden brown.