Melt the butter in a light-colored skillet over medium heat.

Swirl the pan occasionally and cook for 3–5 minutes, until the butter foams, the milk solids turn deep golden, and the butter smells nutty.

Remove the brown butter from the heat just before it reaches a deep amber color.

Arrange the chicken thighs in the slow cooker in a single layer, or as close to one layer as possible.

Sprinkle the dry onion soup mix evenly over the chicken.

Pour in the chicken broth.

Pour the browned butter over the chicken.

Cover and cook on low for 5–6 hours, or on high for 3–4 hours, until the chicken is very tender and the meat pulls back slightly from the bone.

Optional: Transfer the chicken to a plate and pour the cooking liquid into a small saucepan.

Simmer the liquid over medium heat for 5–8 minutes, stirring occasionally, until reduced into a glossy sauce.

For a thicker gravy, whisk 1 tablespoon cornstarch with 1 tablespoon cold water and stir it into the simmering sauce until thickened.

Spoon the sauce over the chicken and serve warm.