In a large saucepan melt the butter & add olive oil.
Add the chopped onion and the ham/ sausage/ Prosciutto. Cook the onion until golden or brown.
Add the diced carrots & celery sticks. Cook over medium heat for 2-3 minutes, stirring occasionally.
Add the tomatoes & bring the soup to boil.
Cook for about 15 minutes, stirring from time to time.
Wash and drain the lentils. Transfer the lentils to the saucepan with veggies, add the broth.
Cook the soup over medium heat 45-50 minutes.
Some types of lentils will absorb more liquid than others. If necessary, add more broth while cooking.
You can substitute the broth with water.
Serve the soup hot with freshly grated Parmigiano-reggiano cheese & parsley.