Start by tying the piece of beef liver to a pot lid using pieces of string.
Next, transfer it to a skillet filled with boiling water over medium heat and let it cook for 5 minutes.
After this time has passed, cut all the liver into smaller pieces, transfer to a food processor and blend everything very well.
Add the butter and blend again until smooth.
In a medium bowl, add the cabbage chopped into thin strips and cover with hot water.
Cover the bowl with plastic wrap and let it soak for 10 minutes.
In a large skillet, over medium to low heat, add a drizzle of olive oil.
Add the onion chopped into small cubes, the crushed garlic cloves and the grated carrot.
Season with one teaspoon of salt, a pinch of black pepper and sauté everything very well for 5 minutes.
In a large bowl, add the liver we prepared, the cabbage, the sautéed ingredients, the oat flour, the eggs, chopped green onions and parsley to taste.
Season with one teaspoon of salt, a pinch of black pepper and mix everything very well until combined.
In a large skillet over low heat add a drizzle of olive oil, the mixture we prepared and spread it out well.
Cover the skillet and let it fry for 10 minutes.
After this time has passed, flip the frittata using a plate.
Add the grated mozzarella cheese, cover the skillet again and let it fry on the other side for another 5 minutes.
Serve.