Brown the chicken
Season the chicken thighs generously with 1 teaspoon of the salt and ¼ teaspoon of the pepper. Heat 1 tablespoon of the oil in a large, heavy cast iron skillet (like the
Everyday Family Pan) over medium-high heat. Brown the thighs until golden in parts but not fully cooked, about 4 minutes per side. Transfer to a plate, cut into 2-inch pieces, and cover with foil.
Cook the vegetables
Add another tablespoon of oil to the skillet, reduce the heat to medium, then add the butternut squash and brown, turning once midway through, until it just begins to soften and is golden on both sides, about 10 minutes total. Add the onion, garlic, sage, and ¼ teaspoon cayenne and cook, stirring, until softened, about 8 minutes.
Make the sauce
Add the flour and cook, stirring, until absorbed, 1–2 minutes. Stir in the milk, stock, remaining teaspoon salt, and remaining ¼ teaspoon pepper. Bring to a boil, then reduce the heat to medium-low and simmer until thickened, 2–3 minutes. Return the chicken and any accumulated juices to the skillet and gently stir to combine.
Add the biscuits and bake
Preheat the oven to 450°F. Combine the Bisquick, milk, and cheddar in a bowl and stir until a wet biscuit dough forms. Scatter the dough over the top of the skillet, about 3 tablespoons at a time (you should have 11–12 biscuits, with plenty of chicken showing through). Bake until the biscuits are deeply golden, the skillet is bubbling, and the surface has darkened, about 12 minutes. Lift one biscuit to check the underside; if undercooked, return to the oven for 1–2 minutes more. Brush with garlic butter, garnish with parsley, and serve hot, making sure everyone gets a biscuit.