Start with a large deep pot and fill it about 1.5 inches deep with oil. Set the burner to Medium heat and heat it until it reaches 350 F/176 C. Use a candy termometer to check it.
While the oil is heating up, cut and remove the skins from the onions and then slice them about 1/4 of an inch wide.
In a medium bowl add the flour, salt, and baking powder. Mix with a fork until well combined. Then dredge/dip the freshly sliced onions in the flour mixture. Set those aside in another bowl or on a plate.
To the flour mixture add the milk and the egg. This will create the batter. Mix until well combined.
Dip the floured onion rings into the batter and coat evenly, then place them on a wire rack to drain the excess batter.
In a pie plate or bowl add the breadcrumbs and then dip the battered slices of onion into the bowl coating each side evenly.
Drop them in the oil and fry them for about 3 minutes or so until they get nice and golden brown. Turn them ocassionaly in the oil using tongs. Remove them from the oil and place on a wire rack or plate with paper towel to dry. Enjoy!