Chop the cabbage.
Pour a little oil into the pan and put the cabbage. Add finely chopped onion and cook over medium heat for 12-15 minutes, stirring occasionally.
Add tomato paste and 100 g water. Season with salt and pepper.
Simmer under the lid for another 10 minutes over low heat.
Cut the rye bread slices into small squares and place in a baking dish. Dry in a hot oven and cool. Serve the cabbage soup in deep bowls or tureens. Sprinkle with croutons before serving and garnish with a sprig of parsley.