It is a rich custard...basically a vanilla pudding, and is the essential component for many classic French desserts including eclairs and other puff pastries, Napoleons, fruit tarts, etc.
Cook's note: The pastry cream can be made a day or two in advance, but do not fill your tart shells until just before serving. Once filled, the tart can be topped with fruit, glazed, and served within half an hour or so.
2 cups half and half
1/2 cup sugar
pinch of salt
5 large egg yolks (with the cordlike strands of egg white protein removed)
3 T. cornstarch
4 T. unsalted butter
1 1/2 t. vanilla extract
Heat half-and-half, 6 tablespoons sugar, and salt in medium heavy-bottomed saucepan over medium heat until simmering, stirring occasionally to dissolve sugar.
Meanwhile, whisk egg yolks in medium bowl until thoroughly combined. Whisk in remaining 2 tablespoons sugar and whisk until sugar has begun to dissolve and mixture is creamy, about 15 seconds. Whisk in cornstarch until combined and mixture is pale yellow and thick, about 30 seconds.
When half-and-half mixture reaches full simmer, gradually whisk simmering half-and-half into yolk mixture to temper. Return mixture to saucepan, scraping bowl with rubber spatula; return to simmer over medium heat, whisking constantly, until 3 or 4 bubbles burst on surface and mixture is thickened and glossy, about 30 seconds. Off heat, whisk in butter and vanilla. Transfer mixture to medium bowl, press plastic wrap directly on surface, and refrigerate until cold and set, at least 3 hours or up to 48 hours.