Avoid milk from spilling
Milk will not spill while boiling if one applies glycerine to the rim of the vessel.
Eggs will not crack
Pierce eggs with a sharp pin before boiling. This way you will prevent them from cracking.
Making potato cutlets?
When boiling potatoes for cutlets add the salt to the water itself as potatoes absorb salt better this way.
Prevent onions from burning, frying
Add a little milk to onions while frying, this will help retain a rich colour and prevent them from burning.
Peaked top in a cake could be because of too much gluten being developed in the mixture either due to using too hard a flour or by overbeating. It could also be due to oven temperature being too high.