Clean, rinse, and peel the carrot, kohlrabi, potatoes, and zucchini. Finely grate all vegetables.
Halve each sausage lengthwise, then cut into 1 cm wide slices. In a bowl, combine the grated vegetables, sausage slices, eggs, and flour. Season with salt, pepper, and grated nutmeg.
Preheat the oven to 100°C (212°F). In a small bowl, mix the sour cream and mustard together, then season with salt and pepper.
Heat the clarified butter in a large pan over medium-high heat. Form the mixture into 8-10 cm diameter patties and fry in batches for 3-4 minutes per side until golden brown. Transfer finished patties to the oven to keep warm.
Arrange the cooked patties on serving plates. Spoon 1-2 tablespoons of the sour cream mixture onto each plate. Drizzle ketchup on top and use a wooden stick to create a marbling effect through the sour cream.