NOTES
For a vegetarian version, omit the ham, use more salt and pepper, and make sure to use vegetable stock or water instead of chicken. For a vegan version, use olive oil instead of butter.
To make this in your slow cooker, add all ingredients (omitting the butter) to slow cooker and cook on low for 8 hours or high for 4 hours, or until split peas are cooked to desired tenderness.
To make this on your stovetop, sauté veggies as instructed in a large pot. After adding the remaining ingredients, bring to a boil, cover, and simmer for approximately one hour (or until split peas are cooked to desired tenderness).
This soup will likely thicken once it cools and is refrigerated, especially if you use a ham bone to make it because of the gelatin. Thin out with water and adjust seasonings as necessary.