Preheat oven to 225°C (or 425°F).

Combine milk and vinegar/lemon juice and let stand for 5–10 minutes to make buttermilk.

Meanwhile, sift together flour, baking powder, salt, and baking soda.

With a pastry blender, cut in the shortening until the mixture forms coarse crumbs. You can substitute butter or bacon lard for some of the shortening if you want.

Add buttermilk from step 2, toss with a fork until blended together into a soft dough.

Turn dough onto a lightly floured surface, kneading it lightly, and folding it into itself a few times to make layers. Roll to 1½-2 cm thickness and use a glass lightly coated with flour to cut out the biscuits. Gather the trimmings and repeat forming and cutting.

Place the biscuits on a baking sheet, about 2 cm apart, and bake for 20 minutes, until golden brown.