Master Instructions1. Combine milk, cream, 1/2 cup sugar, and vanilla seeds and pod in heavy 21/2-quart saucepan set over medium heat. Bring mixture to 175 degrees, stirring occasionally to dissolve sugar and break up vanilla seeds.
2. Meanwhile, beat remaining 1/4 cup sugar and yolks in medium bowl, scraping down sides as needed, until mixture turns pale yellow and thickens so that it falls in ribbons, about 2 minutes with electric mixer on medium-high or 4 minutes with whisk.
3. Remove about 1/2 cup hot milk-cream mixture from pan and slowly whisk into beaten yolk mixture. Gradually whisk thinned yolk mixture back into saucepan. Reduce heat to low and bring mixture to 180 degrees, stirring constantly, about 5 minutes. Custard should be thick but not curdled or boiled.
4. Remove saucepan from heat; pour custard through fine-mesh strainer and into nonreactive bowl or container. Retrieve vanilla pod from strainer and add to custard. Place bowl in larger bowl of ice water to bring custard to room temperature.
5. Cover bowl and refrigerate until custard registers 40 degrees or lower on thermometer, 4 to 8 hours. (Custard may be refrigerated overnight.) Remove vanilla pod from custard (or add extract, if using), stir well, and then pour custard into ice cream machine. Churn until frozen but still a bit soft. (Do not overprocess or ice cream may become icy with flecks of butter.) Transfer ice cream to nonreactive container, seal, and freeze until firm. (Ice cream will keep up to 2 days.)