In a large pot, saute the onion, leek, celery, carrots, and garlic over a medium heat until they are translucent. Add in the split peas, the broth, the thyme and rosemary and bay leaves. Bring to a boil, then turn back down to a simmer. Simmer covered for about 45-55 minutes. Skim off any foam from the top. Add in the potatoes and cook for another 30-40 minutes or until peas are softened and to desired consistency. Stir frequently to prevent solids from burning at the bottom. Salt and pepper to taste. Serve hot.