Cook milk in a heavy saucepan over medium heat, stirring often, just until bubbles appear; remove from heat. Add vanilla bean; cover and let stand 20 minutes. Remove vanilla bean from milk; using the tip of a small sharp knife, scrape vanilla bean seeds into milk. Discard vanilla bean pod.
Whisk together egg yolks and next 4 ingredients in a large bowl until thickened. Gradually whisk warm vanilla milk into yolk mixture; return to saucepan.
Cook over low heat, whisking constantly, 20 minutes or until a thermometer registers 160° and custard coats a spoon. Remove from heat; pour through a wire-mesh strainer into a bowl. Cool at room temperature about 30 minutes, stirring occasionally. Stir in whipping cream and eggnog; cover and chill 1 hour.
Pour custard mixture into freezer container of a 1-gallon hand-turned or electric freezer. Freeze according to manufacturer's instructions. Pack freezer with additional ice and rock salt; let stand 1 hour before serving. Yield: about 2 quarts.