In a glass bowl, soak the liver in the milk for 30 minutes
Combine flour, salt and pepper in a small bowl
In a large skillet over medium heat, fry off the bacon and remove and reserve 2 tbsp bacon grease
Return the skillet and bacon grease to the stove, and bring to temprature
Add the onions and fry until soft. Remove from pan and set aside.
Drain the liver coat it in the flour mixture
Fry dusted liver in remaining bacon grease (if the skillet is dry, add a little vegetable oil first).
Once the bottom is golden brown, flip, add the onions back on top, and brown the second side.
Remove and cover.
Add leftover flour to the drippings (no more than two tablespoons), whisk to form a roux, and loosen the fond from the bottom of the skillet. Add the stock and whisk, and heat until pan gravy forms.
Serve the liver with a side of mashed potatoes, and smother with the gravy. Garnish with the fried bacon.