Garlic Rosemary Chicken

Preheat oven to 400°. Drizzle a teaspoon of olive oil over garlic and wrap in foil. Bake until golden and soft, about an hour. Set aside to cool, then pick out cloves. Set aside. In a large skillet over medium-high heat, heat remaining 2 tablespoons oil. Season chicken breasts with salt and pepper, then sear until golden, about 8 minutes per side. Transfer to a plate. Return skillet to medium heat, add more oil if necessary, then add mushrooms. Season with salt and pepper and cook until slightly wilted, 5 minutes. Add butter and let melt, then stir in the garlic cloves, white wine, chicken broth, and rosemary. Bring to a simmer, nestle back in chicken, and let simmer until sauce has reduced slightly, 6 to 7 minutes. Stir in spinach and lemon juice and let cook until spinach is slightly wilted, about 2 minutes more. Serve with mashed potatoes.