Instructions

1. To make the filling: Place the sweet potatoes and garlic cloves in a small pot and add water until they are barely covered. Bring pot to a boil over medium heat and cook for 8 to 10 minutes, or until potatoes are fork tender. Drain the water from potatoes and set the pot aside.
2. While the potatoes are cooking, in a mixing bowl, sift the flour and salt together. Make a well in the middle of the dry ingredients, then add the water and oil to them. Knead the dough for 1 to 2 minutes, or until combined, with no dry spots. If the dough is still quite sticky, add a pinch or two of flour at a time and knead some more. Set aside while you finish the filling.
3. Next, add the non-dairy milk, nutritional yeast, dijon mustuard, onion powder, salt, and pepper to the potatoes. Mash the potato mixture until fluffy; taste, and season with more salt and pepper if need be.
4. To assemble: Lightly dust your work surface with flour, and cut dough into 2 pieces. Roll each piece out to roughly 1/8-inch (3 mm) thick. Using a cup or cutter roughly 3.25-inches across to cut circles in the dough.
5. Drop a heaping-tablespoon-sized (roughly 16 g) scoop of filling into the middle of each circle. Lightly wet the outer 1/4-inch (6 mm) of the dough rounds with water, then fold them in half. Seal the edges together by pinching them with your fingers or pressing down with a fork.
6. Bring a large pot, filled with roughly 2 quarts (1895 ml) of water to a boil over medium-high heat. Once at a rolling boil, place 6 or 7 pierogi in the water. Do not overcrowd the pot, as they will expand slightly, boil pierogi for 3 to 4 minutes, or until they start floating on the top of the water and are opaque.
7. Place the cooked pierogi on a baking sheet, and repeat boiling process with remaining pierogi. (At this point, you can either freeze the pierogi for later, eat them soft, or fry them to serve.)
8. To serve: In a skillet, warm 1 tablespoon (15 ml) oil over medium heat. Add onion slices, stirring to coat in oil, then adjust heat to medium-low and cover with lid. Start batch-frying the pierogi per instructions below, and between each flip, stir the onions as well. Once you're on the last batch, add a hefty pinch of salt to the onions, stir, adjust heat to low, and cover; cooking until brown throughout.
9. In a large skillet, warm 1 tablespoon (15 ml) oil over medium heat. Once hot, add 5 pierogi to the skillet and brown for 3 minutes on each side; repeat 3 more times with remaining pierogi. Set fried pierogi on a paper towel-lined baking sheet. Once all are fried, divide the pierogi between 4 plates, serve with yogurt and garnish with scallions.