Place the chicken thighs in a bowl and pour the buttermilk over them, ensuring they are fully submerged to marinate for at least 30 minutes in the refrigerator.
In a shallow dish, whisk together the arrowroot powder, almond flour, smoked paprika, garlic powder, onion powder, sea salt, and black pepper until well combined.
Remove each chicken thigh from the buttermilk, letting the excess liquid drip off, then dredge thoroughly in the flour mixture until every surface is coated.
Heat the avocado oil in a large cast-iron skillet over medium-high heat until the oil is shimmering and hot.
Carefully place the chicken in the skillet and cook for 6-8 minutes per side, turning only once, until the exterior is deeply golden and the internal temperature reaches 165°F.
Transfer the chicken to a wire rack to rest for 3 minutes to maintain the crunch before serving.