Preheat oven to 350° Fahrenheit. Grease a large 9x13" baking dish with vegan butter. Tear brioche buns into pieces and place them in the baking dish.
Combine soy milk, sugar, and the rest of the vegan butter in a microwave-safe dish and microwave about 30 seconds to melt the butter. Mix in the cinnamon and stir until the sugar is dissolved, then pour mixture over the bread pieces.
Use a spoon to press bread down to absorb the liquid. Keep pressing all over until all of the bread is moistened. Spread blueberries over the top.
Bake for 15 minutes, uncovered. Allow to cool 5 minutes before serving. Serve with maple syrup or vegan whipped cream. You can optionally top it off with a dusting of powdered sugar.
Calories: 91kcal | Carbohydrates: 13g | Protein: 1g | Fat: 4g | Saturated Fat: 1g | Trans Fat: 1g | Cholesterol: 1mg | Sodium: 49mg | Potassium: 47mg | Fiber: 1g | Sugar: 12g | Vitamin A: 318IU | Vitamin C: 3mg | Calcium: 35mg | Iron: 1mg