1. Prepare an ice bath; set aside. In a small saucepan, heat the milk over medium-high heat just until bubbles form around the edges and the milk starts to steam, about 4 minutes. Turn off heat.

2. In a medium bowl, whisk together sugar and egg yolks until pale and thick, about 2 minutes. Slowly add hot milk, whisking constantly. Strain mixture through a fine sieve back into pan.

3. Place pan over medium-low heat; cook, stirring constantly, until custard is thick enough to coat the back of a spoon and leaves a bulging mark when you run your finger through it, 10 to 12 minutes. Stir in vanilla, and transfer to a clean bowl. Place in ice bath to chill, stirring occasionally. Serve, or store in an airtight container in the refrigerator up to 3 days.