Bring first 3 ingredients to simmer in heavy medium saucepan over medium-low heat. Remove from heat, cover and let steep 40 minutes.

Return half and half mixture to simmer. Beat sugar and egg yolks to blend in medium bowl. Gradually whisk in hot half and half. Return mixture to saucepan. Stir over medium heat until custard thickens slightly and leaves path on back of spoon when finger is drawn across, about 7 minutes; do not boil. Pour into large bowl. Refrigerate custard until well chilled.

Scrape any seeds remaining inside vanilla beans into custard. Transfer custard to ice cream maker and process according to manufacturer's instructions. Freeze ice cream in covered container. (Can be prepared 1 week ahead.)

Makes about 8 cups.