Wash the fillets and dab dry. Clean, peel and wash carrots. Cut 1 carrot lengthwise into wide strips with the potato peeler. Peel and chop the garlic. Heat the oil. Sauté garlic in it.
Fry the carrot strips for about 1 minute. Take out and let drain. Keep garlic oil. Cover 1 fillet with carrot strips. Add the second piece of meat. Pin the open sides vertically with wooden skewers.
Then wrap the woods with kitchen yarn. Cut 200 g carrots into large pieces. Bring the fillets and carrot pieces to the boil in a saucepan with lightly salted water and the garlic oil (the fillet should be just covered with liquid) and let it boil for about 12 minutes at low heat.
In the meantime, sort, wash and roughly chop the spinach. Peel and finely chop the onions. Cut the rest of the carrot into small cubes. Melt the fat in a pot. Sweat flour in it. Add cream and 300 ml of the cooking liquid while stirring and bring to the boil.
Season to taste with salt, pepper, lemon juice and horseradish. Cook the spinach and carrot cubes for about 5 minutes at medium heat. Remove the wooden skewers and kitchen string from the meat and carefully cut the fillet open.
Serve with the sauce on a preheated plate.