Soak Dal and Rajma Overnight.
Next morning, throw away that water, rinse well and put 8 cups boiling water along with all the ingredients,EXCEPT milk, on High setting, in the crockpot. Make sure to cover with lid.
You don't even need to stir the first 2-3 hours. Keep stirring , every hour after that.
Meanwhile prepare Tarka/Vaghar
In hot Ghee, add jeera/cumin. Once it splutters, add chopped onions.
Once onions turn golden, add 2 tbsp Ginger,(save the other 2 tbsp, we will use it later) and garlic and continue to cook till the raw smell of ginger garlic goes away
Add in the kasoori methi and stir
Add crushed tomatoes/tomato puree lal mirch and garam masala and cook till Ghee separates. When ghee separates that means tarka is ready.
Meanwhile, Once you see that the water and Dal are no longer separated and have incorporated into a thick consistency, add the tarka and give it a good stir.
Add milk, stir and cover and bring to a boil. Cook till flavors blend in and the dal milk and tarka are all blended in. This can take about an hour or more
Add the remaining 2 tbsp of minced Ginger in the end.