In a large pot, heat the olive oil over medium heat. Add the onions, celery, carrots, thyme, and garlic. Season with salt and pepper and sauté, stirring occasionally, for 5 minutes, until the vegetables start to soften.
Add the broth to the pot along with the bay leaf and split peas, and bring to a simmer. Lower the heat so the soup stays at a simmer and cook for about 1 ¼ to 1 ½ hours, until the split peas are very tender and starting to fall apart.
Taste and adjust seasonings as needed. Serve in bowls, sprinkled with Parmesan if desired.
Notes
Do Split Peas Need to Be Soaked Before Cooking?The short answer is no, they don’t. They are a fairly soft legume, so cook fairly quickly. Split peas cook in about an hour and a half, but if you want to shorten the cooking time and have the ability to plan ahead, soaking them in water to cover for several hours can speed up the cooking time. If you soak them for 24 hours, the cooking time should be reduced to about 45 minutes.Storage and Reheating
If you make your split pea soup a day ahead and refrigerate it, you will see that it will thicken up considerably. When it’s reheated, it will loosen up again but still be thicker than when you first made it. If this is what you were looking for, great. If it’s too thick, just add some more broth or even water. Vegetarian split pea soup will last for about 5 days in the fridge.
It can also be frozen for up to 6 months. Make sure to leave some space in the soup container when you seal it up, as the soup will expand a bit when it freezes.