Melt the butter over a medium/low heat, then bloom 1 tsp whole cumin seeds until fragrant (about 1 min) then add the onions and a pinch of salt. Fry for around 8 mins, until they're nice and soft.
Add minced garlic and ginger, sauté 3-4 mins more until the raw aroma has subsided.
Add 1 tbsp olive oil in the centre, then the spice mix. Fry for one minute more.
Add the tomato purée. Coat well in the spice mixture
Add the lentils and the stock. Mix well, season to taste.
Simmer on a medium heat, lid off for 30min-1hr (this allows the flavours to really get to know each other, but you can eat it straight away too) Remove the bay leaves and cinnamon stick. Allow to cool a little then blitz half the mixture with a stick blender, of if you don't have a stick blender scoop out some of the dal with a cup measure or mug and transfer into a blender. Pulse until chunky, then pour back in. Mix well and top with more butter and cream.
