Trim the crusts from the bread, break it into large pieces, and place in a medium bowl. Cover with water, then immediately grab the pieces of bread and squeeze most of the water out of them with your hands.
Put the bread, fish roe, and garlic in a blender or food processor. Turn on the blender to thoroughly combine the roe and bread.
Mix the olive oil and vegetable oil together in a measuring jug.
With the motor on the blender running, gradually pour the oils into the fish roe mixture, until it has all been added. Add the lemon juice and white pepper. Taste, and add more lemon juice if desired.