Melt 1 tablespoon butter in a medium skillet over high heat; add mushrooms, and sauté 10 minutes or until mushrooms are browned and liquid is evaporated.
Add 1 tablespoon butter, garlic, and shallots to skillet; sauté 5 minutes. Stir in Marsala and chicken broth, stirring to loosen browned bits from bottom of skillet. Bring to a boil, and cook 20 minutes or until reduced by two-thirds. Remove from heat, and stir in remaining 1 tablespoon butter.
*1 (8-ounce) package sliced button mushrooms may be substituted.