Fill the steamer stock pot with about 2-4 inches of water (you don't want water in the steamer pan)
When water starts to boil and create steam, add lobster and cover, turning heat to medium heat and steam for 14 minutes
When the lobster is done, remove it from the pot and cut down the middle lengthwise with a very sharp knife. Remove the green intestinal part of the lobster before serving.
Sauce
In a saucepan add the olive oil and green onions, sauté over medium-high heat for 3 minutes, add the garlic and sauté for 1 minute more. Add the vinegar and let reduce until there is very little liquid left.
Add the wine and let reduce by half. Meanwhile, add the cornstarch to the tablespoon of water. Add the half and half and the cornstarch mixture to the pot. Stirring continually.
Remove from heat as soon as it starts to boil. Salt and pepper to taste.