If I understand your question correctly, then you're looking for Ras Malai to-go, not dine-in.

Pakistan Sweets (Hilwayat Pakistan) next to the Arab Bank round about between Sofitel & Sooq Waqif has decent Ras Malai to-go. I don't know if it's the "best" Ras Malai in town, but it's certainly one of the most famous. My issue with it is that it's a bit too sweet for my taste and its milky sauce is a bit too thick.

If you're into fast-food style Ras Malai, then Family Food Center sells a very ligh Ras Malai that's not as sweet or as thick in term of sauce, but it's also not as good quality as Pakistan Sweets. It's main advantage is that it's a very easy taste to accept (not an acquired taste) and it's very light.

Finally, if you want dine-in places, then the Indian/Chinese restaurant in Ramada Hotel has the best of both worlds: light, very well prepared, and its sweetness is just right. However, they don't sell it to go. You'd have to dine at their place; if you do, you're guaranteed the best Ras Malai in Qatar. Unfortunately the name of the restaurant escapes me, but it's the only Indian/Chinese restaurant in Ramada, and although they claim to be Chinese too, 99% of their food is Indian.

Hope this helps.