Preheat the oven to 450° F. Prepare the dutch oven with a sheet of parchment paper that covers the bottom and comes up the sides enough to prevent the dough from touching.
Measure out soy milk and pour in apple cider vinegar. Stir. After a few minutes, this will turn to "buttermilk".
In a large bowl, whisk together flour, baking soda, and salt.
Add the buttermilk and stir until it can be worked with your hands. Knead the dough until it comes together into a ball.
Place the ball on the parchment paper inside the dutch oven and score an X approximately 1/4" deep across the top. This will allow the dough to expand while baking.
Cover and bake for 20 minutes.
Turn temperature down to 400° F and bake for another 20-30 minutes. When tapped on the bottom of the loaf, it should sound hollow.