In a shallow bowl, whisk together the soy milk, pumpkin puree, potato starch, brown sugar, vanilla, cinnamon, and pumpkin spice powder. Whisk again right before dipping; the starch settles fast.
Dip each side of the brioche quickly. Brioche is softer and sweeter than sturdier breads, so do not let it soak or it will fall apart.
Melt vegan butter in a pan over medium heat (not medium-high; brioche browns fast). Cook each slice about 2-3 minutes per side, until golden brown.
Serve warm with your favorite toppings, like maple syrup.
Notes
Potato starch and cornstarch work interchangeably here, 1:1.If you don't have pumpkin spice powder you can make your own by combining ground cinnamon, ginger, nutmeg, allspice, and cloves.