Step 1

Split vanilla beans lengthwise with a sharp paring knife. Gently scrape out all the seeds.

Step 2

Place vanilla-bean scrapings and pods in a medium saucepan with milk. Scald the mixture, cover, and remove from heat. Let steep for 30 minutes.

Step 3

Combine egg yolks and sugar in the bowl of an electric mixer fitted with the whisk attachment. Beat at medium-high speed until very thick and pale yellow, 3 to 5 minutes. Alternatively, whisk together in a medium bowl.

Step 4

Return milk to stove, and bring just to a simmer. Using a measuring cup or ladle, slowly pour about 1/2 cup of the hot-milk mixture into the egg-yolk mixture, whisking constantly on low speed until blended. Keep adding milk mixture, about 1/2 cup at a time, until it has all been added. Whisk until combined.

Step 5

Pour mixture back into saucepan, and cook over low heat, stirring constantly with a wooden spoon, until mixture is thick enough to coat the back of a spoon, 3 to 5 minutes. The custard should retain a line drawn across the back of the spoon with your finger.

Step 6

Fill a large bowl with ice and water. Remove pan from heat, and immediately stir in chilled cream to stop the custard from cooking. Pour through a mesh sieve into a medium bowl set in the ice bath, and stir occasionally until cooled. (Discard vanilla-bean pod and strained seeds.) Stir vanilla extract into cooled custard. Cover bowl, and transfer to refrigerator until chilled, at least 30 minutes or overnight.

Step 7

Pour custard into an ice-cream maker, following the manufacturer's instructions. Churn until the ice cream is just set, but not hard.

Step 8

Transfer soft ice cream to an airtight plastic container; freeze at least 4 hours and up to 1 week.