Using sharp kitchen shears, carefully slice through the upper shell of each lobster tail, extending the cut down to the tail’s base. While cutting, slice slightly into the top portion of the flesh.

Turn the tail over and gently crack the underside transparent ribs to help ease the shell open.

With fingers and thumbs, gently part the shell and lift the lobster meat upwards, detaching it slightly from the shell while keeping the base connected. Rest the meat above the shell, exposing it for even broiling.

Adjust the oven rack to the upper-third position so that the lobster meat will be situated about 6 inches from the broiler element. Preheat the broiler to high.

In a mixing bowl, combine the chopped parsley, crushed garlic, mustard, salt, black pepper, olive oil, and lemon juice. Stir well to create a marinade.

Set the prepared lobster tails into a roasting pan (either 9x13 or 8x12 inches). Spoon the marinade evenly over the exposed meat of each tail. Dot each with ½ tablespoon of butter, broken into small chunks and spread over the surface.

Place the pan under the broiler and cook for 10 to 11 minutes, or until the meat turns opaque and white throughout. An instant-read thermometer should register 145°F in the thickest part of the tail. Once broiled, move the lobster tails to a serving dish and sprinkle with additional parsley if desired.

Pour the cooking juices from the roasting pan into a small saucepan. Add the remaining 2 tablespoons of butter and bring to a gentle simmer. Once melted and warmed through, remove from heat.

Serve the sauce poured over the lobster tails or portion it into small ramekins for dipping.