Once all the pieces have been covered in flour in a sautee pan add in 1 tb of the olive oil and melt 1 tb of the butter over medium heat. Cook the onions till golden brown all over stirring occasionally (about 10 minutes).
Once the onions are golden brown add in the 1/2 cup of sherry and cook till reduced by 1/2. Remove from the heat and set aside.
In another sautee pan heat another tb of olive oil and melt the remaining tb of butter over medium heat. Add in the liver pieces and cook 2 minutes. Flip the pieces and cook for another minute.
Remove the liver pieces from the pan to another pot. Deglaze the pan with the remaining 2 tb of sherry and scrape to free up all the stuck bits. Add in the onion mixture and stir to combine everything.
Garnish the liver pieces with parsley. Serve and enjoy!