1. If using gel-canister ice-cream maker, freeze canister overnight.
2. Place a large bowl and strainer on heatproof surface near stove. Split vanilla bean. Scrape out seeds, then add seeds and bean to a heavy, nonstick, medium-size saucepan. Add milk and yolks to saucepan. Stir in sugar. Cook over medium heat, stirring constantly with rubber scraper, until instant-read thermometer just reaches 160 degrees F. to 170 degrees F., about 15 to 20 minutes (do not let boil), or until slightly thickened. Strain immediately into bowl; stir in salt and vanilla extract.
3. Place plastic directly on surface of custard to prevent skin from forming. Refrigerate until chilled, about 4 hours.
4. Add cream to custard, stirring to combine. To freeze, pour in ice-cream maker; process as per manufacturer's directions for about 30 minutes. Scrape into a 1-1/2-quart container; freeze to firm completely, at least 3 hours.