Place whole psyllium husk in a medium sized mixing bowl.
Pour in 200g of water and still well to combine. Let it sit for about 10 minutes, allowing it to absorb the water and form a gel.
Whisk together the flours, onion seeds, salt, sugar and baking powder in a large mixing bowl.
Add half of the melted butter, yoghurt and egg to the psyllium husk gel and whisk together until smooth.
Add the wet ingredients to the dry ingredients and bring the dough together with your hands. Tip the dough out onto a clean work surface and knead into a smooth ball. The dough will be a touch sticky but not enough that it sticks to your work surface. Then divide the dough into 4 (about 150g each) and roll into individual balls.
Heat up a cast iron skillet or wide flat bottomed pan to maintain a medium heat.
Dust the work surface and a rolling pin with extra cassava flour then roll each dough ball out into a teardrop shape, 8 inches in length. Shape and pat the dough for a nice even look.
Heat each naan in the hot dry pan for about 3 minutes on each side or until brown spots start to appear underneath.
Remove from the heat and brush one side of each naan with the rest of the melted butter and sprinkle with coriander and extra sea salt. Serve immediately.