Preheat the oven to 450°F. Lightly oil 48 mini muffin cups.
Put the garlic cloves in a food processor and pulse until finely chopped. Add the quartered mushrooms to the processor and pulse until finely chopped.
Transfer the mixture to a bowl. Change the blade on the food processor to the grater attachment and grate the cheese; transfer to a separate bowl.
Cook the chopped bacon in a heavy skillet over medium heat, stirring occasionally, until browned, about 5 minutes. Add the mushrooms and garlic and cook, stirring occasionally, until the mushrooms are deeply browned and the moisture they have released has evaporated, about 15 minutes.
Remove from the heat and season with salt and pepper to taste. Stir in the parsley.
Whisk together the eggs and milk.
To assemble, put a pinch of shredded cheese in the bottom of each oiled muffin cup.
Divide the mushroom mixture evenly among the muffin cups (about ½ teaspoon per cup), followed by the egg mixture (about 1 tablespoon per cup).
Bake the quiches until puffed and golden brown, 15 to 18 minutes. Let the quiches cool for 10 minutes before running a knife around the edge of each quiche and popping it out.
Serve right away or, to serve later, transfer the quiches to a parchment-lined baking sheet and freeze until the quiches are frozen firm. Transfer the quiches to an airtight container and store in the freezer for up to 1 month. To reheat, bake in a 400°F oven until warm through, 8 to 10 minutes.