Vanilla sugar is simply sugar in which vanilla beans have been stored for several weeks; the vanilla flavor and aroma infuse the sugar, making it a delicious addition to many recipes.
In a small saucepan over medium-high heat, combine milk, heavy cream, and vanilla bean with scrapings. Bring to a boil. Remove from heat, and let steep for 1 hour.
In a large bowl, whisk yolks, vanilla sugar, and salt to combine. Bring milk mixture to a boil, and remove vanilla bean; reserve for another use. Slowly add to yolks while whisking constantly. Let stand 5 minutes.
Prepare an ice-water bath: Fill a large bowl with cold water and ice. Add vanilla extract to the ice-cream base, stirring to combine. Strain through a fine sieve over a medium bowl. Set bowl with ice-cream base in ice-water bath to cool, about 30 minutes. Transfer to an ice-cream maker, and freeze according to the manufacturer's directions.
Prepare vanilla sugar about a week before making the ice cream: Immerse two vanilla beans in a pound of granulated sugar; allow to infuse in an airtight container until ready to use. Plain granulated sugar may be substituted.