Melt butter in a large dutch oven over medium heat. Add onion and 1 tsp of the salt. Cook until onions are soft and golden, about 10 minutes. Add ginger, garlic and chillies. Saute until they soften, 1-2 minutes. Add the spices and cook until fragrant, a minute more.
Stir in the tomato, cauliflower and potato. Season with 1 ½ tsp more salt and add 2 cups of water. Stir again, cover and bring to a boil on high heat, then reduce heat slightly and simmer for 10 minutes, stirring occasionally. Uncover and continue cooking until vegetables are soft and sauce has reduced, 5-7 minutes more.
Video
Notes
Coarsely mash some of the potatoes in the pot with a wooden spoon to thicken the sauce more, if you like.
As written, this is a medium-hot spice level. Use one fresh chilli and omit the cayenne if you like a mild-medium dish (you can always add more cayenne at the end).
I like this ratio of a bit more cauliflower than potato to keep the dish on the lighter side (because I like to double down on carbs with a pile of soft, homemade butter naan). Flip the ratio to 4 cups cubed potato and 3 cups cauliflower if you prefer it heartier (you don’t have to change anything else).
For a little tang, add some amchur (dry mango powder) along with the spices or a splash of lime juice/ lemon juice at the end.
I prefer yellow or red potatoes because they hold their shape.
Add a handful of frozen green peas at the end to boost the veggie content with a pop of green.