2012 hyundai sudden burst cloud of whit smoke what caused it

SOURCE: sudden whit smoke

it is a blow head gasket. the coolant circulating around in the block is kept out of the cylinder by the head gasket. the coolant burns white and that is what you see out the exhaust pipe. i would recommend not driving the car with this problem because you can hurt other engine parts **** as spark plug and you risk over heating.

SOURCE: slow to start when it does start there is a cloud

If its black smoke, I'd suspect that you either have some leaking injectors or worn valve seals. White smoke would indicate coolant getting into the combustion chambers (head gaskets?) I'd pull a few plugs to see if they have anything on them before starting it up after sitting overnight.
a weak ignition coil or a coolant or manifold air temp sensor can do much the same thing though so I'd do some testing to see what you are dealing with before buying any parts. (check air filter as well...if it's really dirty it can contribute to that.)
You didn't mention any coolant loss or overheating so I'd tend to lean towards the engine getting a rich mixture or one of the other items related to that I mentioned.
Haynes and chilton are decent when it comes to sensor testing instructions and all you need is a digital multi-meter. Fuel pressure gauges are expensive so you may want to consider borrowing or having a shop check pressure for you. (Older gauges for carbureted engines read too low to help)
Good luck