Make the coating by mixing the egg and milk in one bowl then placing all the dry coating ingredients int another bowl and stir to ensure they are combined.
Prepare the onion by remove the outer skin then remove a one inch center core using an apple corer but do not core completely the way through. You need to leave the root at one end in tact to hold the onion together.
Slice through the onion again not going to the bottom but just three quarters of the way down, rotate the onion 90 degrees then repeat and repeat twice more turning the onion and slicing.
Pull the sections apart to open the onion up then dip it into the milk and egg mixture. Immediately dip it into the flour mixture and ull apart the sections of the onion and sprinkle the flour mixture inside to ensure an even coating then repeat again by dipping in the milk mixture and again into the flour mixture.
Using a deep sided pan, heat 3 inches of oil in the base of the pan to 350ºF / 180ºC degrees, place the onion into the hot oil with the root at the base then after 3-4 minutes, turn to cook the other side.
Once golden and crispy remove from the oil and set onto kitchen paper to drain the excess oil.
To make the dipping sauce mix together all the ingredients and serve on a platter with the blooming onion flower.