It will be 13 years (on Christmas Day) since I left England, and so it's at least 13 years since I last had a good Mulligatawny. Here in the USA you can not even buy tinned Mulligatawny, because (allegedly) it had beef in it and the Americans are petrified that they will get mad cow disease from any beef imported from England...
My recollection of it is as a spicy, curried barley soup, so start with this recipe (and see how far off my memory is):
Ingredients
4 cups chicken stock
4 cups vegetable stock
1/2 cup pearl barley
2 tbsp ghee
1 tbsp garam masala
1 tsp ground cumin
1/2 tsp ground coriander
1 tsp turmeric
1 tsp cayenne pepper
Directions
Melt the ghee and fry the ground cumin, ground coriander, turmeric, cayenne pepper and garam masala, for about 30 seconds.
Add 1/2 cup of barley and coat the barley with the ghee and spice mixture.
Add 4 cups chicken stock.
Simmer for 30 minutes, stirring, to make sure the barley does not stick to the bottom of the pan.
Add 4 cups vegetable stock.
Simmer for 30 minutes
The reason I add two kinds of stock at different time is because the first time I made it I only added the 4 cups of chicken stock so it reduce too far down, and the starch from the barley thickened it up too much, so (since I only had vegetable stock left). I liked this, so I kept the recipe. The stock I use (here in the USA) is the Kitchen basics brand (which is the lowest in sodium, at 14%), so you don't get that 'dry' sensation in your mouth, like after eating tinned or packaged soup.
I suspect that it needs thin strands of chicken and also needs to be either clearer or requited more turmeric (to give it a more yellow colour)
I'd LOVE to hear from others who can suggest improvements, and to make it authentic.
It's still lacking something, but it's good (especially on cold days...of which we get very few, here is Las Vegas!!!).