In a bowl slice up the sweet onion (I used mandoline to thinly slice the onion, you can use a knife) to the thickness you want and separate the onion rings. Divide the milk in half and soak the onion in it for about one hour ( it removes the onion smell, this is optional)

Drain the milk and toss the onion in flour (like half a cup) and place on a cooling rack or a bowl., and set aside.

If you want it a little bigger, you can also do that as shown in the picture.

Heat enough oil over medium-high in a fryer or a pot to about 365 degrees F. While the oil is heating, in a bowl mix cornstarch, paprika, cayenne with the remaining flour. In a separate bowl, whisk milk and egg together.  Mix the dry and the wet ingredients together. 

Coat the onion rings with the batter in small batches and fry immediately until crisp and golden. Make sure you turn about 2 minutes. 

Let the oil heat up before frying the next batch until you finish all the coated onions. Season with salt and serve. Here's how the thin-sliced looks like

...and this is a little bit thicker. You can combine your sauce, sour cream, ranch dressing, ketchup, or a mixture of any of the ingredients. Enjoy!