Lightly coat a 6-quart or larger slow cooker with nonstick spray.
To the slow cooker, add the carrots, potatoes, Italian seasoning, salt, cayenne, and 3 cups chicken broth. Stir to combine.
Cover and cook on low for 6 to 8 hours or high for 3 to 4 hours, until the potatoes and carrots are completely tender.
While the vegetables cook, in a medium bowl, whisk together the evaporated milk and cornstarch until no lumps remain. During the last 30 minutes of cooking, add the cornstarch/milk mixture. Continue cooking for 30 additional minutes.
Just before serving, stir in the shredded cheddar and sour cream. With a potato masher or large spoon, mash half of the potatoes directly in the slow cooker. The soup will continue to thicken as it cools.
If you would like the soup to be thinner, add the remaining 1 cup chicken broth until you reach your desired consistency (warm up the broth first). Stir to combine, then season with salt and pepper to taste.
Serve hot, topped with bacon, chives, and additional cheese/Greek yogurt as desired.
