Soak the split peas in cold water for about 1 hour; drain and rinse.

Add the drained peas to a large pot with the ham bone, cold water, sliced onions, kosher salt, black pepper, dried marjoram, and bay leaves.

Bring to a boil, then reduce heat and simmer for 90 minutes.

Remove the ham bone, pick off the meat, and return the meat to the pot.

Add the carrots, chopped celery, and diced potato; simmer until the vegetables are tender.

Use an immersion blender to blend the soup to your desired thickness and heartiness.

Serve immediately while warm.