Butter-Poached Lobster (Beurre Monté)

Bring a large pot of heavily salted water to a rolling boil. The water should taste like mild seawater. Dispatch each lobster humanely by driving the tip of a heavy chef's knife through the cross on the back of the head. Plunge the lobsters headfirst into the boiling water. Blanch for exactly 2 minutes — this sets the shells to brilliant red and makes the meat release from the shell cleanly, but leaves the interior essentially raw. Transfer immediately to an ice bath. Once cool enough to handle, twist off the claws and knuckles. Using kitchen shears, cut down the underside of the tail shell and pull the raw tail meat out in one piece. Crack the claws with a lobster cracker or the back of a heavy knife and extract the claw meat in whole pieces. Keep the knuckle meat connected to the claw if possible. Pat all meat very dry with paper towels. Season lightly with fine salt. Any moisture on the surface will break the beurre monté when you add the lobster.

In a small, deep saucepan, bring the water to a simmer over medium heat. Once simmering, begin whisking in the cold butter cubes two or three at a time, adding each new addition only after the previous cubes have almost entirely emulsified — the liquid in the pan should remain creamy-yellow and opaque, never separating into a greasy pool. Maintain a temperature between 82–88°C (180–190°F) — hot enough to melt butter, cool enough to keep the emulsion intact. Use an instant-read thermometer. Add the smashed garlic clove and tarragon sprigs to infuse while you build the emulsion. The finished beurre monté should be glossy, homogeneous, and coating — holding on a spoon like a loose cream sauce. Make at least 450 g of butter's worth to ensure enough depth in the pan to submerge the lobster meat completely. Keep warm over the lowest possible heat, or a double boiler.

Using a thermometer, verify the beurre monté is holding at 82–85°C (180–185°F). Gently lower the lobster tails and claw meat into the butter, making sure they are fully submerged. Baste continuously with a large spoon, ladling the warm butter over any exposed surfaces. Poach for 5–7 minutes for tails, 3–4 minutes for claws. The goal is internal temperature of 60°C (140°F) measured at the thickest part of the tail — this produces silky, just-set meat. Do not let the pan exceed 90°C or the proteins will seize and the texture will become rubbery. Remove from heat and allow to rest in the butter off heat for 1 minute. Lift with a slotted spoon. Squeeze a few drops of lemon juice into the remaining beurre monté, whisk briefly, and spoon it over the plated lobster as a sauce. Finish with a pinch of fleur de sel and fresh tarragon leaves.