Preheat oven to 375 degrees and grease a rimmed sheet pan or large baking dish
Toss chicken thighs with olive oil, 2 teaspoons garlic, salt, and pepper.
Melt butter in a large skillet over medium-high heat. Add 2 tablespoons honey and give it a quick stir to coat the pan. Add chicken thighs and cook 1-2 minutes on each side to brown the outside. (See note for alternate method)
Transfer chicken to your prepared baking pan/dish.
Toss mushrooms with remaining 2 tablespoons butter (melted), 1 teaspoon garlic, and some salt and pepper. Add to the sheet pan along with the chicken.
Bake for about 15 minutes until chicken is cooked through and mushrooms are tender. While chicken cooks, prepare the balsamic glaze.
In a medium sauce pan combine balsamic vinegar and brown sugar. Give it a good stir, bring to a boil over medium-high heat, then reduce heat to a simmer 8-10 minutes until reduced by half and thickened enough to coat the back of a spoon. Stir in remaining 2 tablespoons honey and pinch of salt.
Drizzle balsamic glaze over chicken and mushrooms, garnish with fresh basil if desired and serve.