In same saute pan, over low heat, add shallots and garlic and cook until aromatic. Add mushrooms and stir.
In a measuring cup, measure out wine, if using, and chicken broth. Turn the heat up to high, and deglaze the pan with the broth mixture until starting to reduce.
Remove the pan from the heat and finish the sauce by whisking in butter. Season with salt and pepper, to taste.
Spoon the sauce over the chicken and serve.