Either in a medium bowl with a hand mixer, or in a stand mixer with a whisk attachment, whip the aquafaba in a small bowl for 3 minutes until foamy.

Add the vegan butter, plant-based milk, flour, brown sugar, baking powder, salt, and turmeric. Mix in the stand mixer with a dough hook, or by hand on a clean work surface for 4-5 minutes until a smooth dough forms. Cover the bowl containing the dough with a plate and let it rest at room temperature for 30 minutes.

Meanwhile, place the potatoes in a pot and cover with water. Bring to a boil over high heat, then reduce to a simmer and cook for 15-20 minutes until fork-tender. Drain and transfer to a large bowl.

Mash the potatoes until smooth, then mix in the vegan sour cream, vegan cheddar, salt, and black pepper.

In a skillet, melt the vegan butter over medium-high heat. Add the diced onions and cook, stirring frequently, for 9-10 minutes until golden brown and soft. Add the caramelized onions to the mashed potato mixture and stir until fully combined. Let the filling cool to room temperature.

Cut the log into 2-inch (5 cm) sections. Pinch and twist the open ends of each piece to seal, then place them seam-side down on the prepared baking sheet. Flatten each piece slightly with your hand.