Heat oven to 375 degrees F. On a lightly floured board, roll out the pastry dough 1/16-inch thick. Using a 3-inch cutter, cut out 42 circles; re-roll scraps as needed. Fit circles into bottoms and slightly up sides of lightly greased 2-1/2-inch muffin pans. Meanwhile, fry bacon slices until crisp. Drain and crumble or chop. Chop mushrooms and saute in butter until limp and liquid evaporates. Combine bacon, mushrooms, green onion, and cheese. Divide filling equally among muffin cups. In large bowl, beat together eggs, add sour cream, and stir until smooth. Spoon about 1 Tbsp. into each muffin cup. Bake until puffed and light brown, 20–25 minutes. Cool in pans 5 minutes; lift out. Serve warm or let cool on wire racks. If made ahead, wrap cooled quiches airtight and refrigerate overnight. Reheat, uncovered, in a 350-degree oven for about 10 minutes. Makes 3-1/2 dozen.