Dice bacon in ¼ inch cubes. Place in a heavy 6-quart pot over medium-low heat. Cook until fat is rendered and translucent (reserve some bacon to top the soup). Add onion, carrot, celery, and garlic. Cook until onion and garlic are soft and translucent. Season with salt and pepper.
Add split peas, stir to coat with fat. Add bay leaves and stock. Increase heat and bring to a boil. Reduce heat to a simmer. Skim foam that rises to the surface for about 10 minutes, until no more appears. Add thyme. Simmer uncovered for 1 hour or longer, until peas are soft and starting to fall apart.
Remove soup from heat. Add salt and pepper to taste. Remove bay leaves. Puree the soup until just short of smoothness.
