To a large mixing bowl, add the flour, sugar, salt and yeast and mix together to combine.
Add the cold sliced butter and mix in with a spatula until the vegan butter slices are coated. Be careful not to break up the butter slices.
Add the cold soy milk and stir together until a shaggy dough forms.
Transfer the dough to your clean counter surface and use your hands to form the dough into a ball (the dough may look dry, but it will hydrate as it chills). Wrap the dough tightly in plastic wrap and chill in the fridge for 1 hour.
Once the dough has chilled, place it on a flour-dusted surface and flatten it into an approximate rectangular shape with your hands. Then roll the dough with a rolling pin into a ½ inch thick rectangle shape.
Fold the dough by folding the bottom up into the center and then fold the top down over the first fold. Then turn it a quarter turn so that it’s vertical. With a rolling pin flatten it into a rectangle.
Now repeat the folding process. Fold the dough by folding the bottom up into the center and then fold the top down over the first fold. Then turn it a quarter turn so that it’s vertical. With a rolling pin flatten it into a rectangle.
Repeat two more times (four times in total), until the dough has large streaks of vegan butter through it but is smooth and flat. (If at any point the dough starts to feel warm and not workable and sticks to the counter, chill it in the fridge for 10 - 15 minutes).
Fold the dough one last time (fifth time), but don’t roll it out. Wrap the dough tightly in plastic wrap and chill for 1 hour.
Line two baking sheets with parchment paper and set aside.
Once it has chilled, remove the plastic wrap and place the dough on a flour-dusted surface and divide it in half. Roll one portion out at a time in a long rectangle shape (Approximately 8 x 15 inches). Cover the second portion with plastic wrap and place it back in the fridge until you finish with the first one.
With a pizza cutter (or a sharp knife), cut the dough into three even rectangles. Then cut diagonally across each rectangle to form long, skinny triangles (about 5 inches long on the wide end of the triangle).
Now form your croissants. Place a triangle in front of you with the wide end facing you. Notch the wide end in the middle with a ½ inch cut, then roll from the notch outward (wide end) to the pointed end, tucking the point under the croissant.
Place your rolled croissants on a parchment-lined baking sheet, 6 per baking sheet and cover loosely with plastic wrap. Allow to proof at room temperature for 1 and ½ hours or until doubled in size. Then repeat this process with the second half of dough.
After the croissants have proofed, place the covered trays back in the fridge for 30 minutes. It’s best to bake the croissants cold from the fridge.
Preheat the oven to 375°F (190°C) and brush the croissants with soy milk before baking.
Bake for 18 to 20 minutes until golden brown and flaky. Bake one tray at a time and leave the remaining tray in the fridge until the first tray is done baking.
Cool completely before enjoying your homemade croissants.