Preheat oven to 425 °F.
Combine soymilk and vinegar and let stand.
Mix dry ingredients in a large bowl.
Add the soymilk mixture and the oil, and stir until just blended.
Spread the batter into a nonstick or lightly oil-sprayed 9-inch square baking dish, and bake for 25 to 30 minutes, or until a toothpick inserted in the center comes out clean.
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