Preheat oven to 400 degrees. Line a rimmed baking sheet with parchment paper.

In a small bowl, whisk together oat milk and cider vinegar to make vegan buttermilk. Mixture will clabber — it’s supposed to). Set aside.

In a food processor, sift together flour, cornstarch, baking powder and salt. Pulse a time or two to combine.

Pulse in the chilled vegan butter and mix quickly, just until mixture becomes like coarse meal. Pour in vegan buttermilk and give a quick mix to form a damp dough.

Dust rolling surface generously with flour. Turn out the biscuit dough, and pat out or roll out to 1/2-inch thickness. Flour the rim of a glass or use a floured 2-inch or 3-inch biscuit cutter to form biscuits.

Place biscuits on the rimmed baking sheet. Brush tops with melted vegan butter, if desired.

Bake for 15 minutes. Biscuit should be lightly golden, pillowy and fragrant.