Prepare Chicken - Trim excess skin and fat from the chicken thighs. Season both sides with salt and pepper.
Sear Chicken - Place a large skillet over medium-high heat. Once hot, add olive oil. Add the chicken skin-side down. Sear until golden brown, about 5 minutes. Flip and continue cooking for 2 minutes. Transfer to a clean plate.
Add Vegetables - To a 6-quart slow cooker, add onions, carrots, potatoes, corn, and garlic. Add the seared chicken on top of the vegetables, plus thyme, and rosemary.
Prepare Sauce - In a medium-sized bowl, whisk together 1 teaspoon salt, ½ teaspoon black pepper, chicken stock, flour, and lemon juice. Add the sauce to the slow cooker.
Slow Cook - Cover and cook for 2 to 4 hours on the High setting, or 4 to 6 hours on the Low setting, or until the chicken is cooked through and potatoes are tender.If desired, place the chicken on a sheet pan and broil to crisp the skin (see notes).
To Serve - Transfer the chicken and vegetables to serving plates. If desired, strain the sauce liquid, and season with salt and pepper. Serve the meal with lemon wedges and sauce.
Crispy Chicken Skin: To make the skin on the chicken crispy again after slow cooking, transfer the chicken to a foil-lined sheet pan. Brush lightly with olive oil and broil in the oven about 10 inches from the upper heating element, about 3 to 7 minutes.
Make it Gluten-Free: Substitute all-purpose flour with 2 1/2 tablespoons arrowroot powder, or 3 tablespoons cassava flour. Alternatively, make a slurry by mixing 1 1/2 tablespoons cornstarch and 3 tablespoons water. Mix it into cooking liquid in the last 45 minutes of cooking.
Storing: Cool and store in an airtight container for up to 5 days.
Reheating: Cover and microwave on high setting in 30-second increments until hot.