With the whisk attachment, start whisking mixture on low for about 30 seconds, then gradually start increasing speed to medium. Whisk on medium for one minute, until mixture is white and starting to become fluffy. Raise speed to high for 2-3 more minutes until stiff peaks are formed. Best way to check this is to keep your eye on the whites. Once they get glossy and you start seeing streaks formed by the whisk, it might be time to stop.