In a mixing bowl, sift together the flours, baking powder and salt. Work the buttery spread in with the tines of a fork until the mixture has the texture of a coarse meal.
Add the nondairy milk and sweet potato and work them in to form a soft dough.
Turn the dough out onto a well-floured board and knead for 2 to 3 minutes, adding a small amount of flour if the dough is too sticky.
You can either roll the dough out and cut into 2- to 3-inch circles, gathering up and rolling out remaining dough until used; or divide the dough into 12 or more equal pieces and shape into balls, then flatten each lightly.
Arrange on a parchment-lined baking sheet and pat them down a bit to flatten. Bake for 15 to 20 minutes, or until a toothpick inserted into the center of one tests clean. Transfer the biscuits to a rack or plate to cool.