Pour the warm water and milk into a large glass bowl. Sprinkle the yeast over the water. Let stand until bubbly, about 5-10 minutes.
Add the salt, the rest of the sugar, oil and half the flour. Mix with a wooden spoon until blended. The dough at this point will be sticky.
Add the rest of the flour and continue mixing until the dough forms into a ball and leaves the sides of the bowl.
Transfer the dough to a floured surface (a large wooden board is best). Knead the dough with your hands by folding it then pushing it with the base of your palm. Knead for 10 to 15 minutes or until the dough is elastic and just a bit sticky.
Dust with more flour as you knead if necessary.
Lightly oil the sides and bottom of a large glass bowl. Gather the dough into a ball and place it in the bowl, rolling it few times to coat the entire surface with oil. Cover with a damp cloth and leave to rise for an hour. The dough will double in size.
Meanwhile, prepare the filling. Heat the cooking oil in a skillet. Saute the garlic and onion until fragrant. Add the corned beef. Season with salt and pepper. Cook for 3-4 minutes or until the mixture is quite dry.
Transfer the sauteed corned beef to a sieve, with a bowl underneath, to drain well.
Punch down the dough and transfer to the floured wooden board. Knead for a few minutes.
Divide into four portions. Roll each portion into a log. Divide each log into 4-5 pieces.
Using your hand, cup the dough and make circular motions until the dough is round.
Take one piece and flatten with the palm of your hands. Place a teaspoon of the sauteed corned beef at the centre of the dough. Gather the edges and pinch to seal well.