Create the Tangzhong by combining white bread flour with non-dairy milk in a saucepan. Whisk continuously until thickened, about 3-5 minutes. Remove from heat and cool slightly.

In a large bowl, combine the cooled tangzhong, cold non-dairy milk, sugar, vanilla extract, salt, and instant yeast. Gradually mix in remaining flour until shaggy dough forms.

Knead the dough for 8-10 minutes until smooth and elastic. Place in an oiled bowl, cover, and let rise for 1-2 hours.

Preheat oven to 180°C (350°F). Roast rhubarb with sugar and orange juice for about 10 minutes until softened.

After dough has risen, punch it down and divide into 10 pieces. Shape into discs and let rise for 30-45 minutes.

Prepare the frangipane filling by whisking ground almonds, cornstarch, sugar, and melted vegan butter until smooth.

Spoon frangipane filling into each bun, top with roasted rhubarb, and brush edges with non-dairy milk or syrup.

Bake for 20-25 minutes until golden brown. Allow to cool slightly.

Glaze with reduced rhubarb juice before serving.