In the bowl of a stand mixer fitted with a dough hook, combine flour, sugar, yeast, and salt. Knead on low for 30 seconds.

In a large liquid measuring cup, whisk together the milk, egg, egg yolk, and butter.

Pour the wet ingredients into the well in the dry ingredients and knead on medium-low for 10 minutes until smooth and elastic.

Cover the dough with plastic wrap and refrigerate overnight.

In a medium saucepan, whisk together ¼ cup of granulated sugar and the milk. Cook over medium-low heat, whisking continuously until the milk begins to steam, then reduce heat to low.

In a medium bowl, whisk together the egg, cornstarch, and remaining sugar. Temper this with the hot milk mixture.

Pour the egg mixture into the saucepan and bring to a boil over medium heat, whisking continuously, then remove from heat.

Add butter, passion fruit, and vanilla to the mixture and whisk until smooth.

Pour the pastry cream through a fine-mesh sieve into an airtight container and press plastic wrap against the surface. Cool completely and refrigerate overnight.

Line a half sheet pan with parchment paper and flour generously. Uncover the dough and tip onto a floured counter.

Roll the dough into a rectangle about ½-inch thick and cut out 6 circles with a 3-inch round cookie cutter.

Place circles on the prepared sheet pan, cover loosely with plastic wrap, and let rise for 1 hour.

Fill a heavy-bottomed pot or deep-fryer halfway with vegetable oil and heat to 365°F.

Line a wire rack with paper towels and place the sugar for assembly in a shallow bowl.

Transfer chilled pastry cream into a piping bag fitted with a Bismark tip.

Fry 2 donuts at a time for 2 minutes on each side until golden brown. Move to the wire rack with a slotted spoon.

Toss each donut in sugar while still warm.

After 15 minutes, use a skewer or piping tip to poke a hole in the side of each donut and fill with pastry cream until plump.

Serve warm or at room temperature.