Use to make Candied Kumquat Tartlets.
Place milk and 1/4 cup sugar in a large heavy-bottomed saucepan over medium heat; cook until just barely boiling. In a large bowl, whisk together egg yolks with remaining tablespoon sugar until thickened; sprinkle in flour and cornstarch and continue whisking until well combined.
Slowly pour half the hot milk mixture into the egg yolk mixture, whisking constantly; transfer egg yolk mixture to remaining milk mixture in saucepan, whisking to combine. Place over medium-high heat and bring to a boil, whisking constantly until thick.
Strain through a fine mesh sieve into a large bowl; stir in vanilla. Rub surface of pastry cream with butter to prevent a skin from forming and cover with plastic wrap, pressing down on surface of cream to cover. Transfer to refrigerator until chilled. Gently fold in whipped cream just before using.