Rinse the lentils and cull them for small stones and debris.
Heat oil in Dutch oven or heavy large saucepan over medium-high heat.
Add sausage and brown, about 5 minutes. Remove from pot and set aside. Do not dump oil.
Add onion and sauté until translucent, about 7 minutes.
Add garlic, continue to sauté, about 2 minutes.
Add lentils to pot; add broth. Mix in curry and a pinch cayenne.
Add bay leaf if using.
Bring to a boil, then reduce the heat and cook at a lively simmer for about an hour, stirring from time to time to prevent the lentils from burning.
Add water or broth as needed if liquid cooks down too quickly.
After about 40 minutes (when lentils are not quite done but almost), add chard. It will cook down quickly.
Taste to correct seasonings; add salt if needed.
Add more broth or water to desired thickness (I like mine very thick).
When the lentils are cooked and the chard is tender, serve piping hot in bowls. Top with sour cream if desired.
