Preheat a pan over medium-high heat and add the butter and oil. The oil prevents the butter from burning. Add the turkey filets and don't move them until it has cooked ¾ of the way (yo usee this by noticing the change in colour from pink to white). Flip them and cook them on the other side for 2 extra minutes.
Remove the turkey from the pan and add the onion, paprika and oregano to the same pan where we cooked the turkey. Cook the onion over medium heat until it's very soft and starts to get golden. As it cooks you can cut the turkey in cubes.
Add the garlic and cook it for 30 seconds - 1 minute, stirring constantly.
Add the wine (optional) and let it evaporate completely.
Add the flour and mix.
Add the milk and cream and mix. Add the cubed turkey (also add the jiuces it might have let go of) and let everything simmer over low heat until the sauce thickens.
Correct the level of salt and pepper and serve.