In a medium mixing bowl whisk the egg yolks until they lighten in color. Gradually add the sugar and whisk to combine.

Place the half-and-half and the heavy cream and salt into a medium saucepan, over medium heat. Bring the mixture just to a simmer, stirring occasionally, and remove from the heat.

Temper the cream mixture into the eggs and sugar by gradually adding small amounts, until about a third of the cream mixture has been added. Pour in the remainder and return the entire mixture to the saucepan and place over low heat. Continue to cook, stirring frequently, until the mixture thickens slightly and coats the back of a spoon and reaches 170 to 175 degrees F. Pour the mixture into a container and allow to sit at room temperature for 30 minutes. Stir in the vanilla extract.

Place the mixture into the refrigerator and once it is cool enough not to form condensation on the lid, cover and store for 4 to 8 hours or until the temperature reaches 40 degrees F or below.

Split the vanilla bean in half, lengthwise, to expose the tar-like seeds inside the pod. Scrape the seeds loose with a knife; add the bean and the seeds to the cream mixture.

Heat the cream over medium-high heat until just at a boil. Remove from the heat. Gradually pour the hot liquid into the yolks, while whisking constantly. Return the cream-egg mixture to the saucepan. Cook over medium-low heat, stirring the mixture constantly, with a wooden spoon in a figure-8 motion, until thickened, about 10 minutes. When the ice cream mixture is properly cooked it should coat the back of a spoon, be satiny thick, and be free of any bubbles on the surface. (If you taste the ice cream base it should have a slight egg-y taste.) When thickened, pour in the reserved milk to prevent the mixture from overcooking. Strain into a medium bowl. Add the cognac if desired.

Fill another bowl with ice. Set the bowl of ice cream base in the ice and stir until thoroughly chilled. Freeze the base in an ice cream machine according to the manufacturers instructions. (Take care not to over churn the ice cream or it will get a grainy texture.) Transfer the ice cream to the freezer to set up for at least 1 hour. Serve.