In a large bowl, combine the flour, baking powder and salt. Cut in shortening until mixture resembles coarse crumbs. In another bowl, mash the sweet potatoes and milk. Add to the crumb mixture just until combined.
Turn onto a floured surface; knead 8-10 times. Roll to 1/2-in. thickness; cut with a 2-1/2-in. biscuit cutter. Place on ungreased baking sheets.
Bake at 425° until golden brown, 8-10 minutes. Remove to wire racks. Serve warm.