In a large skillet over medium - high heat, heat 1 tablespoon oil. Add chicken, season with salt and pepper, and sear until golden, 3 minutes per side.

Meanwhile, in a large slow cooker, toss potatoes with remaining 2 tablespoons oil, butter, garlic, thyme, parsley, and Parmesan and season generously with salt and pepper. Add chicken and cook for 4 hours on high, or 8 hours on low, under potatoes are tender and chicken is fully cooked.

Garnish with Parmesan before serving.