Peel and cut your potatoes into chunks. Bring a large pot of water to a boil and cook your potatoes until they are fork tender. Reserve 1/2 cup of the water that the potatoes boiled in and then drain the potatoes.
Using a potato masher, mash the potatoes until they are smooth. Add a bit of the reserved water if you need some liquid to make the potatoes easier to mash. Allow to cool.
In the bowl of an electric mixer, fitted with the paddle attachment, combine the mashed potatoes with the vegetable and olive oil. Mix until well combined and then add the grated onion and the lemon juice. Mix until well combined and your mixture is smooth and free of any lumps.
Stop your mixer and then spoon in your tarama. Turn the speed back up to medium and mix until just combined. You will need to use a rubber spatula to scape down the sides. If you find that your taramosalata is too thick, fill the jar which your tarama came in with cold water and shake it. Then, add up to 6 tablespoons of this water to the taramosalata until you get the texture that you like.
Store your taramosalata in the refrigerator.
Enjoy!