In a jar or other deep container, put in the caviar, very finely chopped onion and salt to taste (about 1/2 tsp). Add the lemon juice and blend. Blend into a smooth mixture and add the pre-soaked and drained middles of 2 slices of bread.
Continue to mash and gradually pour the oil in in a trickle. If you prefer, you can choose not to pour in all of it. Finally, check the taste of the caviar.
If needed, add more salt and beat with the ground cloves.