Place butter in a medium bowl along with garlic, truffle oil, herbs, lemon juice, salt and pepper. Mash and stir until evenly combined. Season to taste with additional salt, pepper and truffle oil.
Using your fingers, evenly spread a heaping teaspoon of truffle butter beneath the skin of each thigh. You should have some truffle butter leftover. Season both sides of each thigh with salt and pepper.
Warm a large cast-iron skillet over medium-high heat. Place chicken in the skillet skin-side down, and cook until the skin is crispy and golden (5 to 10 minutes). The chicken may pop and splatter. Use an outdoor burner or splatter screen to keep your kitchen clean! Flip each thigh, then transfer the skillet to the oven. Continue to cook until the chicken registers an internal temperature of 165°F (about 10 minutes more). Let rest for 5 minutes before serving.