In a large pot, melt butter (or heat olive oil) over medium heat. Add onion and carrot, cook until softened, about 5 minutes.

Stir in tomato paste and cook for another minute.

Add lentils, broth, cumin, paprika, and red pepper flakes (if using). Bring to a boil, then reduce heat and simmer for 20-25 minutes, until lentils are very soft.

Use an immersion blender to puree the soup until smooth. If using a regular blender, blend in batches and return to the pot.

Stir in lemon juice and season with salt and pepper to taste.

In a small pan, dry-toast the dried mint over medium heat for about 1 minute until fragrant.

Serve the soup hot, drizzled with olive oil and sprinkled with toasted dried mint.