Remove the crust of the bread and soak in water.  Once done, squeeze out the water as much as possible.

In a blender, place the roe and the onion, the pepper, and the soaked bread.  Blend well.

While the blender is running, add the lemon juice and then the olive oil, poured in a slow stream.

Taste the mixture and if necessary add more bread, olive oil, pepper or lemon to personal taste/preference.