Melt butter in a large pot, then sauté onion, leek, carrots, and celery for 6-7 minutes until softened, stirring as needed so the vegetables cook evenly. Keep the heat at medium to avoid browning the aromatics.

Add garlic, cumin, turmeric, and black pepper and cook for 2 minutes, stirring constantly until fragrant. The spices should look slightly toasted but not dark.

Add rinsed lentils, broth, and ham hock if using, then bring to a boil over high heat. Once boiling, the liquid should be lively with steady bubbles across the surface.

Reduce the heat so the soup maintains a gentle simmer and cook for 30-35 minutes until the lentils are completely tender and falling apart. Stir occasionally to prevent sticking, especially along the bottom.

Remove the ham hock, shred any meat, and return the meat to the pot, then discard the bone. Make sure no bones remain before blending.

Blend about half the soup until smooth and thick, then stir it back together to keep a textured, creamy consistency. Blend carefully in batches if needed, and stop when you reach the thickness you like.

Stir in cream if using and season with salt to taste. Simmer for a minute after adding cream so it blends in evenly and turns silky.

Ladle the soup into bowls and top with fresh parsley and serve with crusty bread for dipping. The surface should look glossy and thick like a hearty stew.