In a pot on medium heat warm the milk up until it starts to gently bubble. Mind to stir it fairly often to avoid burning down. Whilst the milk reaching the boiling temperature; separate the eggs and discard the whites. In a medium bowl whisk the egg yolks for about a minute until light yellow and increased in volume. Whisk in the cornstarch vanilla extract agave syrup and gradually about 1/2 cup of the hot milk. The goal is to raise the temperature of the yolks so it won't get curdled when added into the hot milk. Slowly pour all of the egg yolk mixture into the scalding milk while stirring vigorously until the mixture seems completely liquified. Keep warm and continuously stir until the custard thickens. Serve warm refrigerate or use as preferred.