Melt one tablespoon butter (or heat olive oil) in a large skillet over medium heat. Season chicken thighs with salt and black pepper and transfer four of them to the skillet. Brown chicken, approximately 3 minutes per side, and transfer to a platter.

Repeat process with remaining butter (or olive oil) and chicken thighs. Once browned, transfer the remaining chicken thighs to the platter with the first batch.

Deglaze skillet by adding the chicken broth and gently scraping the bottom with a spatula to incorporate the flavorful brown bits into the liquid. Remove from heat and reserve the deglazing liquid. Set aside.

Add garlic, onion, carrots, and potatoes to a 6-quart or larger slow cooker crock and arrange the browned chicken thighs on top.

Spread 2/3 of the lemon slices over the chicken and pour the chicken broth from the skillet on top. Sprinkle with the crushed rosemary leaves and season with additional salt and black pepper, if desired.

Cover and cook on high for 3 hours or low for 6 hours.

When cook time is complete, discard lemon slices and serve immediately with chopped fresh parsley and the remaining (uncooked) lemon slices, cut into small wedges for garnish. Enjoy!