Prepare compound butter by mixing 6 tablespoons softened butter with minced garlic, chopped tarragon, and a pinch of salt. Roll in parchment paper and refrigerate.

Remove Wagyu from refrigerator 45 minutes before cooking to bring to room temperature. Pat completely dry with paper towels.

Set up sous vide circulator to 135°F for lobster. Season lobster tails with salt and seal in vacuum bags with 2 tablespoons butter and thyme sprigs.

Sous vide lobster tails for 30 minutes. Meanwhile, prepare sauce by sautéing shallots in 1 tablespoon butter until translucent.

Deglaze pan with cognac, carefully flambé, then add bone broth and reduce by half. Whisk in cream and reduce until sauce coats spoon.

Heat cast iron skillet over high heat until smoking. Season Wagyu with salt and pepper. Add avocado oil to pan.

Sear Wagyu for 90 seconds per side for medium-rare, basting with butter. Use thermometer to ensure 125°F internal temperature.

Rest Wagyu under foil tent. Remove lobster from bags, pat dry, and quickly sear in butter for color, 30 seconds per side.