Combine yeast, warm water, and sugar in a bowl and let sit until foamy.

In a large bowl, mix together flour, baking powder, and salt.

Cut in shortening using a pastry blender or your fingers until the mixture resembles coarse crumbs.

Add the yeast mixture and buttermilk to the dry ingredients.

Stir until just combined.

Lightly knead the dough on a floured surface until smooth.

Cover the dough and let it rest for 10 minutes.

Shape the dough into a 7-inch circle.

Place the circle on a greased baking sheet.

Cover and let the dough rise for 30 minutes in a warm place.

Preheat oven to 375°F (190°C).

Cut an 'X' on the top of the dough circle.

Bake for 35 minutes, or until golden brown.

Serve warm.