Make this for our "English Soup" (Zuppa Inglese).
Stir together milk and lemon zest in a small saucepan. Heat over medium-low heat, stirring, just until small bubbles appear at edges. Remove pan from heat.
Put egg and yolks and the sugar in the bowl of an electric mixer fitted with the whisk attachment. Beat on high speed until pale, 3 to 4 minutes. Reduce speed to low. Add flour and vanilla. Beat until just combined. Beat in the hot milk mixture. Raise speed to high; beat 1 minute more. Transfer the pastry cream to the saucepan. Cook over medium heat, whisking constantly, until mixture has thickened, 2 to 3 minutes.
Transfer warm pastry cream to a bowl. Place a piece of plastic wrap directly onto surface. Refrigerate until just chilled, about 2 hours, or up to 1 day.