Put oven rack in middle position and preheat oven to 400°F.
Roll out pastry on a lightly floured surface with a lightly floured rolling pin into a 12-inch square, then transfer to a large baking sheet.
Blend cottage cheese, sour cream, salt, and pepper in a blender until smooth.
Cook bacon in a 10-inch skillet over moderate heat, stirring occasionally, until it just begins to brown, about 5 minutes. (Bacon should be tender, not crisp.)
Remove from heat.
Spread cheese mixture evenly over pastry, leaving a 1-inch border all around. Scatter bacon and onion on top, then sprinkle with parmesan.
Bake until pastry is golden brown, 20 to 25 minutes.
