Soak sliced potatoes and onion in a bowl with cold water and 1 tbsp sea salt for an hour.
Heat the oven to 180 C (360 F). Cut the top of the head of the garlic, place on foil. sprinkle with olive oil, salt, and pepper. Wrap the foil and bake garlic until soft (approx. 25-30 mins). Peel baked garlic and mash in a small bowl.
For the base, mix together the chickpea flour, baking powder, and salt. Add olive oil and mix it with hands until oil is spread equally. Now slowly start adding water, while mixing the dough by hands. You may need more water (or less) depending on the flour quality. Dough should be soft, but not too sticky. Once desired consistency reached, make a ball out of dough, lightly oil it and leave to rest for 8-10 minutes.
Sprinkle a baking sheet with flour, put the dough on top, spread it into a flapjack, sprinkle with more flour on top. Roll out the dough with a rolling pin until thin.
Heat up the oven to 200 C (390 F). Drain potato thins, soak excess of water with a towel. Spread half of the garlic puree on top of the dough, lay potato thins, drizzle some olive oil on top, sprinkle with salt and pepper. Together with baking sheet transfer to a baking tray. Bake for 16-18 mins.
Get the tray out of the over. Lay sliced mushrooms and onions, spread the other half of garlic puree on top. Bake for another 13 mins. Then add basil leaves and bake for another 2mins.
Slice the flatbread on a cutting board and serve it hot or let it cool down. Top with pine nuts and add a salad on a side (optionally).