Remove the sausage from its casing if using links, or prepare your bulk sausage. Break it into small chunks for even browning.
Heat a skillet over medium-high heat until hot and add the sausage. Cook until deeply browned and caramelized, about 5-7 minutes, breaking it apart with your spoon to develop a nice crust.
While the sausage browns, chop the carrots into small rounds and dice the yellow onion finely. This prep helps the vegetables cook evenly and meld into the broth.
Transfer the browned sausage to your crockpot. Add the chopped carrots, diced onion, canned fire-roasted tomatoes (including juice), vegetable broth, thyme, and bay leaf.
Stir everything together with a wooden spoon, making sure the ingredients are evenly distributed. Cover the crockpot and set it to low for 6-8 hours or high for 3-4 hours.
About 30 minutes before serving, peel and dice the Yukon Gold potatoes. Add them into the crockpot, stirring gently to incorporate.
If you prefer a thicker soup, mix 1 tablespoon of cornstarch with 2 tablespoons cold water to make a slurry. Stir it into the crockpot and cook uncovered on high for about 10 minutes until slightly thickened.
Remove the bay leaf, then taste the broth and season with salt and pepper as needed. Add a dash of red pepper flakes if you like some heat.
Let the soup rest for 5 minutes after cooking to allow flavors to meld. Ladle into bowls, garnish with fresh herbs if desired, and serve hot.
