Step 1

Bring 2 cups half-and-half, the almond paste, sugar, salt, and cornstarch to a simmer in a saucepan over medium heat.

Step 2

Prepare an ice-water bath; set aside. Whisk egg yolks, extract, and remaining 1/2 cup half-and-half in a medium bowl; add one-third of the hot half-and-half mixture in a slow, steady stream, whisking constantly. Pour into saucepan.

Step 3

Bring to a boil over medium-high heat, whisking constantly. Cook, whisking, until mixture coats the back of a spoon, 3 to 4 minutes. Pass through a fine sieve into a bowl set in ice-water bath. Stir in butter, several pieces at a time. Let cool completely, stirring occasionally.

Step 4

Put cream into the bowl of an electric mixer fitted with the whisk attachment. Beat on medium-high speed just until stiff peaks form. Fold into custard.