Preheat the oven to 325°F and grease a 9-inch glass pie plate.
Trim the roots and darkest green leaves from the leeks cut the leeks in half, lengthwise and then cut them into bite-sized pieces. Wash the leeks thoroughly in a large bowl of water. We do this step twice because no one likes sandy food! Use a slotted spoon to lift the washed leek pieces out of the water. Place clean leeks on a bed of paper towels, to drain.
In a skillet, cook the bacon and garlic until crisp, over medium to medium-high heat. With a slotted spoon, transfer the bacon to paper towels to drain. Pour out the bacon grease but do not wipe the pan; the leeks with cook in the remainder of the flavorful grease.
Sprinkle the leeks with salt and add to the skillet, which should be heated to medium-high. Stir the leeks frequently until they are softened. When the leeks are soft, place them evenly in the pie pan and add the bacon and garlic as an evenly-distributed layer.
In a medium mixing bowl, stir together the baking mix and pepper and then stir in half of the milk. Once the milk is incorporated, stir in the remaining milk and the eggs. Stir in the cheese just enough to moisten it and break up any clumps of cheese. Pour the batter into the pie plate, covering the leek and bacon mixture. Bake the quiche until a toothpick inserted in the center comes out clean or about 45 minutes. Let the quiche stand for about 15 minutes before slicing and serving, so that it can set up a bit. Serve warm.