Pour canola oil in the bottom of a 10 inch cast iron skillet. Set aside.
1 Tablespoon canola oil
In a small bowl, add white vinegar to the milk and set aside.
1 ¼ cups milk, 1 Tablespoon white vinegar
In a large bowl, combine flour, baking powder, and salt.
3 cups all purpose flour, 1 Tablespoon baking powder, 1 teaspoon kosher salt
Add shortening to the flour mixture and gently mix in with your finger tips until the shortening is the size of peas or so. Do not overmix.
¾ cup shortening
Add milk mixture and stir with a fork, just until combined.
Pour the batter into the skillet. Flatten into the pan, then flip over so both the top and bottom are coated with oil. Gently press the batter into the pan. Cut into biscuits using a pastry scraper or a knife.