It was late, so I was determined to find substitutions in the pantry rather than make a trip to the grocery store. I'm never very rigid with recipes anyway, so "pantry-style" cooking with what's available is common for me.
I was totally out of channa dal, so I just used more urud. I didn't have any tomatoes, but I did have some ranchero salsa I bought originally to make Huevos Rancheros. I was almost out of cumin seeds, so I improvised with caraway. And finally, instead of pure sour cream, I just topped it off with "cream top" yogurt.
Not quite a traditional batch of Dal Makhani, but it still had all that creamy, "stick to your ribs" goodness!