In a heatproof mixing bowl, whisk together the egg yolks, sugar and salt until blended. Form a kitchen towel into a ring and place the bowl on top to prevent it from moving. Gradually add the hot half-and-half mixture, whisking constantly until fully incorporated. Return the mixture to the saucepan and place over medium-low heat. Cook, stirring slowly and continuously with a wooden spoon or spatula, until the custard thickens and a finger drawn across the back of the spoon leaves a path, 8 to 10 minutes; do not allow the custard to boil.