To make the naans, mix the yeast and yogurt with 250ml warm water. Put the flour and salt in a bowl and gradually stir in the yeast mixture until it comes together as a dough. Tip out onto the worksurface and knead for 10 minutes, or 5 minutes in a mixer with the dough hook, until smooth. Put into a clean bowl, cover with oiled clingfilm and leave for 2 hours, or until doubled in size.
Heat 1 tbsp oil in a large pan, and fry the onion and ginger until really soft. Stir in the spices, cook for 1 minute then add the lentils and chana dahl. Add the coconut milk and 800ml water. Bring to a simmer, turn down to a low heat and cook for 1½ hours, covered, stirring gently every so often, adding more water if needed. To freeze, cool the dahl completely, tip into containers and put in the freezer.
When the dough is ready, knead it briefly on a lightly floured worksurface. Cut into 8 pieces and roll each one out to an oval until they no longer spring back. Lay onto oiled baking sheets, cover with oiled clingfilm and leave for 30 minutes until puffy.
Heat the oven to 240C/fan 220C/gas 9. Heat another baking sheet in the oven. Transfer the naans, two at a time, onto the hot baking sheet. Cook for 5-10 minutes until the dough starts to bubble and the bottom looks golden. Press them gently back down if they’ve domed too much. Cool under a clean tea towel, then individually wrap in foil and freeze.
To reheat, defrost the dahl in the fridge overnight, and leave the naans on the worksurface to come to room temperature. Heat the oven to 220C/fan 200C/gas 7. Put the dahl into a pan with a splash of water, bring to a simmer and cook until piping hot. Put the naans on a baking sheet, sprinkle with a little water and reheat in the oven for 5 minutes or until warmed through. Brush the naans with clarified butter or ghee, and scatter over some nigella seeds to serve.