Peel and boil the sweet potatoes with piloncillo and cinnamon. Use very little water, just enough to soften, and cover while cooking. Once soft, mash into a puree. Remove any tough fibers from the sweet potatoes; the filling should be very smooth and almost dry. Let it cool while you make the dough.

On the table, make a mound with the flour, baking powder, sugar, and salt. Place the lard in the center and start mixing with your hands. Add water as needed. The dough should not be too wet.

Refrigerate for 15 minutes covered, then roll out, cut into circles, and fill with the sweet potato mixture. Seal with water. Pinch the edges. Brush with the egg. Bake for 25 minutes at 350°F (180°C) until the bottom is not burnt. While hot out of the oven, you can sprinkle with sugar.