Fry the onions, garlic and herbs until the onions are soft and are starting to colour. Remove from frypan and set aside.
Fry the livers until cooked through.
Melt the butter in a saucepan then add the flour. After letting the flour cook in the butter for a minute add the milk a little bit at a time ensuring the paste remains smooth. You will be making a roux sauce base but you want to stop before it becomes liquid. The mixture should still be thick and come away from the sides of the saucepan.
In a blender mix the onions with the roux and blend until smooth. Add the cooked liver. Blend to the desired texture; smooth or chunky.
Line a terrine with baking paper and spoon the pate into it.