Creme Mousseline

Whisk together 1/4 cup sugar, the egg yolks, and salt in a medium bowl. Whisk in cornstarch, 1 tablespoon at a time.

Bring milk, espresso beans if using, and remaining 1/4 cup sugar to a simmer in a medium saucepan over medium heat. Whisk a little milk mixture into egg yolk mixture; whisking constantly, gradually add remaining milk mixture. Return mixture to pan, and bring to a boil, whisking constantly. Cook, whisking, until very thick, 2 to 3 minutes.

Pour through a fine sieve into a bowl; discard solids. Press plastic wrap directly onto surface. Refrigerate pastry cream until cold, at least 1 hour (up to 3 days); beat until smooth before using.

Beat heavy cream until soft peaks form. Whisk half the whipped cream into pastry cream, then fold in remaining heavy cream. Stir in preserves if using.