Add the soy milk and 1 teaspoon of lemon juice to a small bowl and set aside for 5 minutes to let it curdle.
Meanwhile, add all the dry ingredients to a large mixing bowl, and whisk to combine. Then add the curdled soy milk, applesauce, vanilla, lemon juice, and lemon zest and mix to combine. Let the batter rest for 10 minutes.
Meanwhile, preheat the oven to 375 degrees F (190 degrees C) and prepare a muffin pan with muffin liners, or use a nonstick pan.
Add approx. 1 tablespoon of the plain batter to the bottom of each muffin cup. Then use a spatula to gently fold the blueberries into the remaining batter. Divide the remaining batter among the 12 muffin cups and bake for 18-22 minutes, or until a toothpick inserted in the center of a muffin comes out clean.
Remove from the oven and let cool at least 10 minutes before removing the muffins from the tray and transferring them to a cooling rack to completely cool.
While the muffins are cooling, combine the icing sugar and lemon juice in a small bowl. Start with 1 teaspoon of lemon juice and increase as needed. Once the muffins are cooled, drizzle them with the icing.
Weigh your flour for the most accurate results. If you don't have a kitchen scale, you may spoon the flour into your measuring cup and use a knife to scrape off the excess. Do not scoop from the bag!Don't skip making the vegan buttermilk. (Mixing the soy milk with lemon juice.) This enhances the dairy flavour, and makes for a fluffier muffin.Use fresh and active baking powder. Baking powder that is open in your pantry for 6+ months can start to lose its effectiveness.The reason for adding some plain mixture to the bottom of the muffin tins before folding the blueberries into the batter is to prevent most of the blueberries from sinking. If there are too many blueberries at the bottom of the pan, it will be too wet and heavy, resulting in uneven baking.If using the glaze, glaze before serving and not in advance. Do not cover the muffins once glazed. Storing glazed muffins in a sealed container will cause the glaze to melt.Make sure your muffins are completely cooled before glazing. Adding glaze to hot or warm muffins will melt the glaze.Leftover muffins will keep at room temperature, covered or in an airtight container for 2-3 days. Refrigerate to keep up to 5 days. Or freeze for up to 4 months.