In a medium skillet, fry the onion until softened. Add in the garlic, then sauté until fragrant.
Place the onions and garlic in a large stockpot or the bottom of a slow cooker.
Add in the potatoes, broth, vegetables, basil and parsley.
Cook in the crockpot on low for 6-8 hours, on high for 3-4, or simmer on the stove until the potatoes are tender and starting to dissolve sightly.
Whisk the cornstarch into the milk, then whisk into the soup. Add the Velveeta and let it melt, stirring occasionally. When it's melted in completely, add in the spinach and stir. It will wilt in a minute or two.
Once the spinach is cooked, spoon into bowls and serve.