The melt-in-your-mouth succulence of a butter-poached lobster tail really knows no peers. The term "butter-poaching" is a bit misleading: Because butter solids separate from butterfat well before the poaching temperature of 180 to 190 degrees Fahrenheit, you must use a water-supported emulsion. Adding water keeps the butter creamy throughout the cooking process.
Making a Clean Break
Butter-poaching lobster is a specialized technique -- you wouldn't perform the same method on chicken breasts, for example. First, you can't simply submerge lobster tails in melted butter, poach them until cooked through and expect superb results. You must flash-blanch them first by pouring a solution of boiling water and acid over the tails to quickly coagulate the surface of the meat but not cook the interior. Without flash-blanching, the fat between the shell and meat congeals and fuses them together during poaching; if that happens, you can't get the tail meat out of its shell in one glorious piece.
Place the lobster tails in a food-grade container -- you want to pack them in closely without compressing them. Barely cover the lobster tails with cold water, then pour it off into a bowl or measuring cup -- the amount of water it takes to cover the tails is the amount you need to flash-blanch them.
Next, measure the same amount of water you poured off into a saucepan, along with 1/2 cup of white vinegar or lemon juice per quart. This food acid cuts the richness of the lobster fat at its surface and frames its delicate taste. It also whitens the color a bit. Bring the water-acid mixture to a boil and pour it over the lobster tails.
For every 1 pound of lobster, steep it for a timed 1 1/2 minutes. Pull the tails from the water using tongs, and lay them flat on a sheet pan. Let the tails cool to room temperature. Do not hold the tails under cold water after removing them from the acid-water solution -- the 1 1/2-minute steeping time takes carryover cooking into account.
Separation Before Union
After steeping, pull the tails from the water and set them on a tray or plate lined with paper towels. Using a cotton kitchen towel to shield yourself from the hot shell, gently press the tail flat with your palm. Twist the tail fin to the right or left to make an opening to press the meat through with your fingers. Insert two fingers into the tail of the lobster, which will make the tail meat release and exit through the wide end. Set the tail meat aside while you prepare the beurre monte.
The technique of beurre monte -- to mount, or add small amounts, of butter in an immiscible liquid -- defines butter-poached lobster. The technique is fundamental: Heat water to a gentle simmer and add butter, about 1 teaspoon at a time while whisking to incorporate. Control your heat -- if you let the emulsion boil, it breaks.
First, cut 1 pound of butter into teaspoon-sized pieces for every 2 pounds of lobster tails you're poaching, and bring 2 tablespoons of purified water to a simmer for every 2 pounds of lobster tail. With a whisk in one hand and the portioned butter at the ready, drop a pat of butter in and slowly whisk -- let it melt gently; the boiling will subside. Continue mounting the rest of the butter into the water a pat at a time. Check the temperature of the beurre monte using an instant-read thermometer -- 180 to 190 F is the target.
Add the spices and aromatics of your choice as you mount the butter. Don't go heavy with the secondary flavorings -- you want to keep the flavorings simple and true to their subject. A minced shallot and a squeeze of fresh lemon juice provide all a quality lobster tail needs.
Add the tail meat to the beurre monte when the emulsion reaches 180 to 190 F. If you intend to use the tail shells as serving vessels, cook them separately in boiling water until they turn red.
Poach the lobster just until it reaches 140 F -- carryover cooking will bring it to its minimum internal temperature of 145 F.
Remove the lobster from the beurre monte and serve it as is. Or, for a hands-on experience, cut the shell in half lengthwise and replace the tail meat in the bottom half of the shell. Spoon a tablespoon or so of beurre monte over the presentation.