Preheat oven to 400°F.
Arrange the bacon slices on a cookie sheet in a single layer.
When the oven has reached temperature, cook the bacon 15 to 20 minutes until it's golden brown and starting to crisp. Begin checking at 15 minutes to avoid burning. Bacon will crisp up more while cooling.
Transfer the bacon to a paper towel-lined plate to drain and cool.
Reduce the oven temperature to 350°F. Prepare a 9-inch pie plate with nonstick cooking spray or a coating of butter. Set aside.
In a large bowl, whisk together the eggs and half-and-half until fully combined and slightly frothy.
Add the onion, garlic, salt, and pepper to the bowl. Whisk until just evenly mixed.
Roughly chop the bacon and scatter it evenly over the bottom of the prepared pie plate.
Pour the egg mixture gently over the bacon. Sprinkle the cheese evenly over the top.
Bake for 35 minutes, until the edges are golden and puffed, and the center is firm but ever-so-slightly wobbly when you gently shake the pie plate. A knife inserted near the center should come out mostly clean.
Remove from oven and let the quiche cool in the pie plate for 5-10 minutes before slicing and serving.