Add the onion and cook, stirring frequently, until beginning to soften, about five minutes.
Stir in the rice and cook, still stirring frequently, for a couple of minutes, until lightly toasted.
Add the wine and cook, stirring almost constantly, until nearly absorbed. Lower heat to medium if necessary to prevent any hint of burning.
Begin adding the stock by the cupful (or so), stirring from time to time.
Continue adding stock as the rice absorbs it. Risotto is finished cooking when each grain of rice is tender but still has a nice hint of chewy bite, and there's a little bit of delicious starchy broth remaining. (Keep in mind that the broth will thicken as you add the cheese and let the risotto rest for a few minutes after cooking.)
Stir in the cream and simmer briefly, until warmed and incorporated.
Off the heat, stir in the lemon juice, tarragon, parmesan, salt, and pepper. Taste for seasoning.
Stir in lobster meat.
Let the risotto rest for about five minutes before spooning into wide, shallow bowls to serve.
Notes
Arborio rice is an Italian short-grain variety of rice. Its high starch content helps create the risotto's silky, creamy broth. And its superior quality means the grains retain their al dente bite amidst the creaminess. Alternatively, you can use carnaroli rice. It works similarly but has a slightly longer grain, higher starch content, and firmer texture.
Use a dry white wine that you'd be happy to drink (and serve the rest of the bottle at the table, if you like).
Fresh tarragon has a mild anise flavor that complements lobster beautifully. I love it in this risotto, but if you're not a fan, you can substitute other soft herbs, like chives, dill, and/or parsley.
I've given an indication of how much fine sea salt to use, but it really depends on the saltiness of your other ingredients, as well as your personal preference. Taste before adding.
Risotto's combination of firm-tender rice and creamy broth will be at its best shortly after cooking. I don't recommend making it in advance. If you need to, you can parcook it in advance, proceeding though step 6 above but stopping with a couple of cups of broth still to add. Finish right before serving.
Leftovers will keep in an airtight container in the fridge for a week. They'll taste great but thicken up a bit, which is fine. You can reheat in the microwave. Risotto leftovers also make great arancini with fresh goat cheese or mozzarella in the middle.