Make the Tanghzhong. In a medium saucepan, whisk together the soy milk and all-purpose flour. Over medium-low heat, whisk the mixture continuously until it thickens to a paste. It will look like packet mashed potatoes. Once it reaches this consistency, immediately take off the heat and put it in the bowl of a stand mixer.
166 grams Soy Milk, 41 grams All-Purpose Flour
Add in the bread flour, honey, pineapple juice (or water), preferment, granulated sugar, and salt. Using a dough hook, mix the dough on low speed for 1-2 minutes, until the dough starts to mix and combine. Then, mix on medium speed for 4-6 minutes, until the dough starts to smooth out and form a cohesive dough ball around the dough hook. It should not be clinging to the sides.
Sourdough Preferment, 476 grams Bread Flour*, 180 grams Pineapple Juice**, 11 grams Sea Salt, Fine, 42 grams Honey, or agave nectar, maple syrup, or date syrup if you want it truly vegan, 38 grams Granulated Sugar
Leave the dough to rest for 10 minutes, covered with a tea towel. While you wait, cut the vegan butter into small pats. The butter should be at room temperature.
Add the butter. With the mixer on low speed, add the butter one pat at a time, waiting until each pat is incorporated before adding the next pat. Once all the butter has been incorporated, about 5-8 minutes, increase to medium speed. Mix for 2-3 minutes, until the dough is cohesive. It will be a little sticky, but it should be fully incorporated. Remove from the mixer, either leaving it in the mixing bowl or transferring to a new bowl for bulk fermentation.
95 grams Vegan Butter, room temperature
3 sets of stretch and folds every 30 minutes. Let the dough rest for 30 minutes, covered with a tea towel, before beginning the first set of stretches and folds:Using clean, slightly damp hands, scoop the dough from one side and pull upwards, then fold the dough over onto itself. Rotate the bowl 180 degrees and stretch and fold again. Then turn the bowl a quarter of the way, stretch and fold again, then turn the bowl 180 degrees and do another stretch and fold. Go around the bowl one more time, meaning you will have done a total of 8 stretch and folds, or have gone fully around the bowl twice. Leave to rest for 30 minutes, covered. Do the next set of stretch and folds. Scoop on the side of the dough and pull up. Once it stretches without tearing as far as it can go, fold the dough back on top of itself. Turn the bowl 180 degrees and repeat. You should do 8 stretches and folds or go around the bowl twice. Cover and let rest for 30 minutes.
Then, do the last set of 8 stretch and folds (going around the bowl twice).
Allow the dough to bulk rest. Cover the bowl and set it in the warmest spot in your home. Depending on your kitchen temperature, this will take more or less time. For this dough, it usually takes 2-3 hours. Ultimately, you're looking for your dough to be slightly less than double in size. It should be puffy, pulling away from the bowl slightly, and slowly rise back when poked with a finger.
Chill the dough for 25 minutes in the fridge. For the dough to be easier to handle, chill it in the fridge to firm up a bit. While you wait, liberally butter the bottom and sides of an 8x8 square baking pan.