My childhood memories of this soup are more like the first one you describe, but there are so many different versions on the internet that I don't know what would be more authentic.

Mulligatawny is one of those dishes that everyone has their own idea of. I've seen recipes ranging from a thin, but spicy lentil soup to a thick, creamy soup with chunks of chicken and vegetables.

My Williams Sonoma Savoring India cookbook has a version that is quite tasty. I've made it with the garam masala and the curry powder (a choice in the recipe) and the flavor is necessarily quite different. If you use the curry powder, make sure to follow the curry powder recipe they suggest rather than a store-bought version to avoid that flavor we Americans think of as "curry" but which is really just one in a million different spice mixes.

I found the recipe on line, and will include it as a link (saves me typing out a long recipe) but I will type out their recipe for curry powder as it appears in my cookbook.

Curry Powder

Curry powder is used mainly in the dishes of the South. Contrary to popular belief, it is not a single spice, but a mixture of spices. The Western-style curry powder that is stocked on supermarket shelves bears little similarity to the carefully blended, personalized mixtures that Indian cooks favor. The ingredients and their proportions vary between dishes, regions and individual cooks, but the following is a typical blend.

3 T coriander seeds
2 t brown mustard seeds
2 t fenugreek seeds
2 t cumin seeds
1 t black peppercorns
6 whole cloves
8-12 dried red chiles, broken into pieces and seeds discarded
2 T roasted chickepeas (garbanzo beans)
2 T turmeric

In a dry frying pan over meduim-high heat, combine the coriander, mustard, fenugreek, cumin, peppercorns, cloves and chiles. Dry-fry the spices, shaking the pan constantly to prevent them from burning, until they are fragrant, about 5 minutes. Transfer to a small bowl, add the chickpeas and turmeric and allow to cool. When completely cool, transfer to a mortar, blender or coffee grinder reserved solely for spices and pound or process (in batches if necessary) until finely powdered. Use immediately, or store in a tightly sealed glass jar in a cool, dry place for up to 3 months.
Makes 1/2 cup (3 1/2 oz/105 g)

You can find chickpeas already roasted as a snack at Indian grocery stores, or roast your own...there are plenty of recipes to do so on the net.

Here is a link that might be useful: Mulligatawny-Williams Sonoma

Thanks. The soup at the restaurant is divine, but I'm not a good enough customer to be favored with the recipe, I fear, so I'll try some of these tips.

Sometimes, even if a restaurant won't give a recipe, they'll at least tell you the ingredients...then you can check the gazillion recipes for Mulligatawny soup for ones that contain similar ingredients, and then play around a little.

I forgot to say that I've also made the Williams Sonoma recipe using coconut milk and using half and half instead. Both were good, but of course different flavors.

I love Indian style lentils. There are many, many recipes for them and one thing I love is that you eat them thick, as a main or side dish with rice and veggies one night, and then make the leftovers into a soup for the next, thinned with water or stock and freshened with some freshly chopped cilantro and tomatoes (or other herbs/veggies), a dash of tamarind paste or lime juice or maybe some cumin & mustard seeds browned in a bit of oil or ghee. Very healthy too!