For the Donut Dough, first prepare the Tangzhong by taking out ½ cup of the flour & combining it with 2/3 cup (160g) of the plant milk in a small sauce pot
Whisk it smooth over a medium heat stirring constantly until it reaches 150°F on an instant read thermometer.
Transfer to a small bowl to cool to lukewarm to the touch.
Combine the room temperature plant milk with the dry yeast & a pinch of sugar in a small bowl & whisk together, let stand for 5 minutes to prove the yeast
In the work bowl of your electric stand mixer with a dough hook attachment combine all the rest of the ingredients including the cooled tangzhong, the proved yeast/milk mixture & the softened vegan butter. Mix on low speed to form a shaggy dough.
Once the dough comes together increase the speed to medium & mix for 4 minutes.
Add flour as needed to make a soft pliable dough rather than a sticky blob.
The dough should clear the sides of the bowl but not be tough **watch video tutorial for more information and explanation on how the dough should look.
Decrease the speed back to low & mix for another 5 minutes
Transfer the dough to a lightly oiled bowl, cover & rise in a warm spot for about 1 hour or until almost double in size.
Meanwhile prepare the custard by combining the sugar & cornstarch together in a small bowl with a whisk, then add to a heavy bottom medium sauce pot with the plant milk
Bring to a full boil whisking constantly to avoid scorching the bottom, then remove from the heat & add the vegan butter & vanilla bean paste, whisk to melt the butter
Transfer to a bowl and cool in the refrigerator while you finish the donuts.
Once the dough has risen to double, turn out onto a lightly floured surface & roll to 1/2" thickness.
Cut donuts with a 3.5" cookie or biscuit cutter & transfer to a sheet pan lined with parchment paper.
Re-roll the dough scraps gently (you should get 9-10 donuts total out of this recipe)
Brush the donuts with aquafaba & then cover lightly and rise again in a warm spot.
Once the donuts have risen again to almost double preheat the oven to 350°F & bake immediately for approximately 18-20 minutes or until lightly golden brown and no longer raw in the middle.
Cool slightly (they should still be warm) & then plunge each donut into the powdered sugar
With a skewer or something similar, hollow out the centers of each donut & then fill with the cooled vanilla bean custard