Put a medium-sized pan on a medium-high heat with a glug of vegetable oil. Add the red onion, red chilli, garlic paste and ginger paste then cook until the onion starts to turn tranclucent.
Add the ground coriander, ground cumin, turmeric and ground chilli, stir well and cook until the spices are fragrant (don’t burn the spices!)
Add a knob of butter and stir in the tomato purée. Cook for 5 more minutes then spoon the spice mixture into a bowl and set aside.
Using the same pan, add the lentils and the vegetable stock with a knob of butter then stir well, ensuring you pick up any remaining spices that have stuck to the bottom of the pan.
Bring to the boil then reduce to a gentle simmer and cook for 40 minutes until the lentils are soft.
Stir in the spice mixture and cook for a further 5 minutes or so.
Add more water depending on your desired consistency then add the coriander to serve!
An unstructured digest of stuff that I've found on the information superhighway.