As the fish bakes, heat the olive oil in a medium-size skillet over medium heat. Add the garlic and shallots and sauté until translucent and tender, about 2 minutes. Add the wine, increase the heat to medium-high and bring to a simmer. Add the chicken broth, return to a simmer, and cook until the liquid reduces by half, 2 to 3 minutes more. Add the lemon juice, capers, if using, and butter and stir until the butter is melted. Taste the sauce and season with salt and pepper. Place the cooked fish on a serving platter and spoon the sauce over.