Boil potatoes in their skins for 15-20 minutes until fork-tender. Peel and cut into 1.5 cm cubes. Remove skin from blood sausage and cut into roughly 1.5 cm pieces. Peel and finely chop the onion.
Heat lard or oil in a large uncoated pan over medium-high heat. Add onion and cook for 4-5 minutes until golden.
Stir in caraway seeds and pressed garlic. Cook for 1-2 minutes until fragrant.
Add blood sausage pieces and cook for 4-6 minutes, stirring frequently until browned.
Mix in potato cubes and cook for 6-8 minutes, repeatedly scraping up crispy bits from the bottom of the pan and stirring well to combine.
Finely grate the fresh horseradish root and sprinkle over top. Season with salt and pepper and serve.