Heat your oven to 350°F/175°C and prepare your muffin pans (spray with vegetable spray or line with papers).
Make vegan buttermilk by stirring together soy milk and vinegar. Set aside.
In a medium-sized bowl, cream the butter and sugar with a mixer. Add the buttermilk, vegan sour cream, and orange zest. Mix again with your mixer until well-combined.
In a small bowl, combine the dry ingredients (flour, poppy seeds, salt, baking powder, and baking soda). Add to the wet ingredients and stir until just combined.
Drop the batter into prepared muffin compartments and bake for approximately 20 minutes. A tester inserted in the center of a muffin should come out clean. When the muffins are done, remove them from the oven and cool on a wire rack.
For the Orange Glaze
While you’re waiting for the muffins to cool, stir together the powdered sugar and orange juice. Don’t worry if the mixture is a little runny – that’s what we’re looking for. Drizzle the glaze over the muffins.