Wash hands with soap and water.
Scrub the carrots, celery, onions and garlic with a clean vegetable brush under running water. Gently rub spinach under cold running water. Dry with a clean towel. Cut the vegetables and set aside.
Slice the kielbasa on an angle, about ¼-inch thick. Wash hands with soap and water after handling the sausage.
Wash your cutting board and knife.
In a large stockpot over medium heat, add the olive oil and kielbasa. Wash cutting board, counters and utensils after handling the sausage. Wash hands with soap and water.
Brown the kielbasa on both sides, and set aside.
To the pot, add the carrots, celery and onions and cook until the vegetables begin to soften and the onions are translucent, about 5 to 7 minutes.
Add the garlic and cook for 1 minute.
Add the salt, red pepper flakes, sage and thyme, and stir to combine.
Take ½ can of the white beans and set aside. Add the remainder of the white beans to the pot. With the remaining ½ can of beans, mash them with a fork or potato masher. Then add them to the pot and stir. Mashing the beans helps to thicken the stew.
Next, add the chicken stock. Raise the heat to high and bring to a boil. Once the stew is boiling, lower the heat to medium-low and add the kielbasa. Allow the mixture to simmer about 10 to 15 minutes to thicken.
Cook the kielbasa until internal temperature reaches 160 °F on a food thermometer.
Add the vinegar and stir. Finally, stir in the spinach. Cook the stew until it reaches 165 °F on a food thermometer before serving.
Transfer stew to serving bowls and top with grated Parmesan cheese.
Reheat leftovers to 165 °F on a food thermometer before serving.