Cut the potatoes into bite-sized pieces and rinse. Dice the kohlrabi. Peel and slice the carrots. Finely dice the onions and cut the spring onions into small pieces. If necessary, brush off the mushrooms and cut into small cubes.
Put everything together with the broth in the saucepan and cover well with water. Bring to a boil over full heat with the lid on, then continue to steep for 20 minutes over medium heat (stirring occasionally).
Cut the processed cheese into pieces and let it melt in the soup. Season to taste and serve.