Dry the chicken thighs by patting dry with paper towel.
In a small bowl, combine the garlic salt and pepper. Sprinkle on both sides of chicken.
Add 1 to 2 tablespoons of olive oil on cast iron skillet and preheat over medium-high heat until hot, oil should be shimmering but not smoking.
Place chicken thighs into the pan, skin side down. Do not cover with a lid, instead use a splatter screen to contain the oil. Cook without moving them at all for 5-7 minutes to give the chicken skin the perfect crispy sear.
Once the chicken skins are deep golden and crispy, use long tongs to turn flip the chicken pieces over and do the same to the other side.
Transfer the skillet with the chicken to the oven and roast for 10-15 minutes until cooked through. Test the internal temperature of the center of the chicken thighs (avoiding the bone) with an instant read meat thermometer and if it is 165ºF they are done.