Preheat oven to 400°F and move rack to center of oven.
In a large bowl, mix the flour, baking powder, and salt.
Using a pastry blender, cut the cubed butter into the dry ingredients until it resembles coarse crumbs.
Add the diced bacon, shredded cheese, and onion, and stir to combine.
Pour the milk into a well in the centre of the dry ingredients.
Using a wooden spoon, gently stir the mixture until it comes together. If it is too dry, you can add more milk a tablespoon at a time until it comes together.
Turn the dough onto a lightly floured surface and bring the dough together with your hands. With a rolling pin, roll the dough out to a half-inch thickness. Fold the dough in half and roll again, repeating one more time.
Cut the scones using a round biscuit cutter, bring the scraps together, and repeat rolling and cutting. If there is a small bit left, you can form a misshapen little scone with your hands. We use a 2.5-inch cutter.
Alternatively, you can roll the dough into a circle and cut it into wedges with a sharp knife.
Place the scones on a prepared baking sheet, lightly sprayed with non-stick spray. Leave about 1/4 inch space between the scones.
Bake for 18-20 minutes until the scones have risen and are golden brown.