Mmmmmm Lentils and spinach! I have both of these

This one is from "Everyone Likes Sandwiches"
lentil spinach soup
1 c lentils (brown, green or black)
5 1/2 c homemade vegetable stock
1 onion, diced finely
2 stalks celery, diced
1 large carrot, diced
6 cloves garlic, minced
1/2 t dried chili flakes
1 bunch spinach, stems removed & well rinsed
salt & pepper
grated cheese (optional)

In a large pot combine stock, lentils, onion, celery, carrots, garlic and chili flakes and bring to a boil. Simmer until lentils and vegetables are tender, about 20-30 minutes. Add in spinach and add in salt and pepper if necessary. Simmer for another 5 minutes. Serve and sprinkle with cheese, if desired.