Pat chicken thighs dry with paper towels. Season both sides with garlic powder, Italian seasoning, onion powder, paprika, kosher salt, and black pepper.

Heat olive oil in a large skillet over medium-high. When the oil shimmers, add the chicken thighs skin-side down. Sear until the skin is golden brown, about 3 to 4 minutes per side. Transfer the thighs to a plate.

Place the carrots and baby potatoes in the bottom of the slow cooker. Season the vegetables lightly with salt and pepper. Scatter the chopped garlic and sliced shallots over the veggies. Tuck thyme sprigs among the vegetables.

Arrange the seared chicken thighs on top of the vegetables, skin-side up. Pour the chicken broth around the edges of the slow cooker to prevent washing off the seasoning.

Cover and cook on low for 6 to 7 hours or on high for 3 to 4 hours. The chicken is done when it reaches 165°F and the vegetables are tender.

For a glossy finish, remove the chicken and stir the cubed butter into the juices until melted. If you want a thicker gravy, whisk cornstarch with 1 tablespoon cold water, stir into the juices, then switch the slow cooker to high and heat for 10 to 15 minutes until thickened.

Serve the chicken hot over the carrots and potatoes. Sprinkle with chopped parsley if desired.