Pour dry ingredients into a mixing bowl and stir until well combined.
Add eggs, egg yolks, butter and milk. Mix well using a dough hook until well combined. and airy. This should take 6 to 7 minutes.
Place the dough in a warm, dry place to prove for about 30 minutes or until tripled in size.
Remove the dough from its bowl and knead for a few minutes.
Cut the dough into 12 equal parts (approx. 80g each) and roll into nice, even balls. Place on a flat, floured tray and press each ball flat for a few seconds.
Cover the trays with your dough balls and place them in a warm, dry place again to prove for another 30 or so minutes until they have at least doubled in size.
Place the dough balls on the tray in the fridge for 10 minutes.
Place the oil in a saucepan and heat to 160°c. Carefully place some of the dough balls in the oil. The side that was facing up during proving should be facing down in the oil. Place the lid in the saucepan.
Fry for 2-3 minutes then turn the balls to cook the other side for the same time.
Remove from the oil and place on paper towel to remove excess oil.
For the filling
Using a long and skinny piping bag attachment, pierce the Berliner and squeeze a good amount of the jam into the Berliner. If you fill it too much, it will squirt out.
Sprinkle with caster sugar and dust with icing sugar to serve.
Notes
If you don't have a warm, dry place, put the oven on low (30-40°c) and let the dough prove.If you want to make sure that your Berliners are all the same size, use scales to weigh the dough balls. Each should weigh 80g.Placing the risen dough balls in the fridge helps to form a "skin" that will turn a beautiful colour when fried.Putting the lid on the saucepan during frying creates enough heat for the bottom of the dough ball to expand a little. This will mean that you have the characteristic pale stripe in the middle of your Berliners once they are cooked.