Cut the puff pastry sheets into 35 rounds, using a 2-inch fluted pastry cutter, and fill 2 small muffin tins with the rounds. Top each muffin tin with a second muffin tin to secure the puff pastry and form pie shells.
Bake until the pie shells are golden brown and cooked through, 15 to 17 minutes. Let cool.
Meanwhile, coat a large saute pan with olive oil over medium heat and cook the bacon until brown and crispy and the fat has rendered out. Transfer to paper towels to drain.
Add the leeks into the pan, sprinkle with salt and sweat until wilted. Stir in the mushrooms, sprinkle with more salt and saute until soft. Carefully pour in the whiskey and cook until the pan is basically dry. Remove from the heat and stir in the creme fraiche, followed by the bacon.
Fill the pie shells, and serve garnished with chives.