Put the lobster in a pot deep enough to cover it with water. Fill the pot up with water then pour the water into another pot, leaving the lobster in the first pot. Boil the water, then add about 1 Tbs of vinegar for each quart of water (you can eyeball this based on the capacity of the pot you used). Once the water boils, carefully pour it into the pot with the lobster. Let this poach for 3 minutes. Remove the lobster with tongs. Twist off the tail then twist off the claws and return the claws to the hot water for another 5 minutes.
To get the tail meat out, use kitchen shears to cut the underside of the shell, right down the middle between the legs. For the knuckles, use a pair of clean channel lock pliers and apply enough force to crack the shell in several places. Then use your sheers to cut through some of the remaining joint material to get the meat out. For the claws, grab the top claw with one hand and grab the bottom claw with the other. Pull them apart until they separate, carefully pulling the lower clawl off along with the cartilage that runs through the middle of the claw. Then use your channel lock pliers to break the very tip of the top claw off and then crack the rest of the claw to get the meat out.
For my lobster I put the meat in a vacuum sealed bag them submerged it in a 160 degree water bath for 10 minutes. This yielded meat that was almost too tender, so I'd recommend increasing the temperature and decreasing the time, or trying a different method of cooking such as butter poaching or pan searing.
For the mashed potatoes, wash and scrub the potatoes but do not peel. If they are large, cut them in half so they are all roughly the same size. Put them in a large pot and cover with water bringing it to a boil. The reason you cook them with the skin on is to prevent them from absorbing too much water. Turn down the heat to maintain a simmer and cook until a fork is easily inserted into the center of a potato. Drain, then peel the potatoes with a paring knife being careful not to burn yourself. Load a potato ricer with the uni then press into a bowl. Then press the butter into the same bowl. Add the cream and salt and whisk to combine. Press the peeled potatoes into the bowl then gently stir until just combined.
For the hollandaise, find a small bowl (preferably ceramic) that can rest on top of a similarly sized sauce pan. Add enough water to the sauce pan so the bottom of the bowl will be submerged and bring to a boil. Lower the heat all the way to the low setting. With the bowl off the heat, add the water and yolk and whisk until smooth and creamy. Put the bowl on the saucepan and continue whisking until the egg yolk increases in volume, looks pale and is thick. Add the butter one piece at a time, whisking after each addition to combine. Finish by whisking in the yuzu kosho, yuzu juice, sugar and salt to taste.