Add the chicken breasts into a food processor and pulse until the mixture resembles ground chicken, about 1 to 2 minutes.
Transfer the ground chicken into a large mixing bowl. Add in the egg, cornstarch, paprika, garlic powder, onion powder, salt and white pepper. Give the mixture a good mix to combine.
Line a large baking sheet with parchment paper. Set aside.
Using wet or lightly oiled hands, scoop up a portion of the chicken mixture, about 2 tablespoons for large nuggets or 1 1/2 tablespoons for smaller nuggets, and pat into desired nugget shaped.
Transfer the shaped nuggets to the prepared baking sheet. Repeat until all of the chicken mixture is shaped into nuggets. You should end up with 12 large or 14 small nuggets.
Cover baking sheet with plastic wrap and transfer to the freezer to let the nuggets firm up, about 1 hour.
In a small shallow dish, add 1/2 cup flour. Set aside.
In a separate medium mixing bowl, add the remaining flour, cornstarch, baking powder, paprika, garlic powder, onion powder, salt and white pepper. Give ingredients a quick whisk to combine.
Next, whisk in the sparkling water, starting with 2/3 cup. The mixture should have a smooth, pourable consistency that is similar to a crepe batter. If the batter looks to be on the thick side, mix in additional water, 1 tablespoon at a time. For reference, I ended up using the full 3/4 cup sparkling water.
Retrieve the nuggets from the freezer. Working with 1 nugget at a time, fully coat in the flour and return back to the baking sheet.
Heat up the oil in a large frying pan under medium heat to 350F.
Working quickly, use a fork to fully coat the floured nuggets in the wet batter and then add into the heated oil. If needed, use another fork or butter knife to help slide the nuggets off the fork into the oil.
In batches of 4 to 5 nuggets, fry the nuggets for 4 to 5 minutes flipping halfway through cook time. The nuggets are done once it takes on a golden brown color and has a crispy exterior.
Transfer fried nuggets to a paper towel line plate to remove any excess oil. Repeat process until all the nuggets are fried.
Note: To avoid ending up with soft and oily nuggets, the oil temperature should be maintained between 340 to 350F and do not overcrowd the pan. Use a kitchen temperature if you have one.
Serve chicken nuggets immediately while still hot and crispy as is or with a side of fries and your favorite sauce. Enjoy!