Stir pine nuts in a wide frying pan over medium-low heat until lightly browned (about 3 minutes); remove from pan and set aside. Increase heat to medium. Melt butter in pan, then add mushrooms and shallot. Cook, stirring often, until mushrooms are lightly browned (4 to 5 minutes). Add reserved 1/2 cup mushroom soaking liquid and cream. Increase heat to high, bring mixture to a boil, and boil, stirring often, until liquid is reduced by about a third.