Peel, wash and slice the potatoes. Heat 2 tablespoons of oil in a pan. Fry the potatoes over medium heat, turning several times for 25-30 minutes. Wash and sort blueberries. Wash the rosemary, dab dry, put something aside for garnishing.
Remove remaining needles. Peel and finely dice onion. Wash fillet steaks, dab dry, tie round with kitchen string. Heat 2 tablespoons of oil in a frying pan and fry the fillets for 4-5 minutes while turning. Remove, season with salt and pepper and keep warm. Sauté onion and rosemary in frying fat. Add 75 g blueberries and maple syrup, deglaze with 200 ml water and vinegar. Let simmer for 5-8 minutes at high heat. Add 125 g blueberries and heat up briefly. Season potatoes and sauce with salt and pepper.
Sauté onion and rosemary in frying fat. Add 75 g blueberries and maple syrup, deglaze with 200 ml water and vinegar. Let simmer for 5-8 minutes at high heat. Add 125 g blueberries and heat up briefly. Season potatoes and sauce with salt and pepper. Serve steaks with sauce and potatoes. Serve with rosemary set aside