Scoop a nice level ice-cream scoop of your batter and drop it into your oil from an inch or so above the oil. The key to getting a nice round shape is to not let it drip out of the scoop for too long after it plopped into the oil.
Cook each doughnut for around 1-2 minutes, making sure you turn them over if they keep floating on to one side. When they are tanned/golden, remove them from the oil and allow them to drain on some kitchen roll.