This soup is one of those things that improves after sitting overnight in the fridge. If you don't puree it, you may need to add a little water to it the next day before reheating because it tends to condense itself.
I love to make this on a chilly day! It's super easy and will make your house smell fantastic!
Heat a few tablespoons of olive oil in a large skillet and sautee onion until tender. Add sausage and fry till crumbly and crustily browned. Drain and set aside.
Place lentils in a pot and cover with water. Bring to a boil and start throwing in boullion cubes. 1 cube per cup of water, if you want to measure, or just keep throwing them in till you get a nice flavored broth. (Keep in mind that you're going to add curry later, so don't go too heavy on the boullion. You can add more at any time.)
At this point you can decide whether or not to puree the soup. The advantages to puree-ing are a.) you don't have to deal with the husks of the lentils floating around in your bowl or getting stuck in your teeth, and b.) it's kind of fun to chop stuff up with a food processor, or an immersion blender, if you have one (even more fun!).
Reduce heat to simmer and add olive oil, garlic, and sausage. I like to scrape some of the pan drippings into the mix. Yum!
Dump in some curry powder till you get the flavor you want.
Cook until lentils are tender, usually 30 to 45 minutes. (You can leave this soup to simmer for as long as you want.)
About 10 minutes before serving, add cilantro to taste. (The more, the better in my opinion!) You may or may not need any salt. Taste and adjust boullion and curry seasonings if needed. If the flavor is too strong or salty, just add more water.