For dough, combine flour, 1/2 teaspoon salt and baking powder in bowl and mix well. Add canola oil, sour cream and water to flour mixture, and knead by hand or with dough hook in a standing mixer for 8 to 10 minutes. Reserve dough.
For filling, mash potatoes, place in an oven to dry, then remove from oven and reserve to cool. Mix mashed potatoes, goat cheese, red onion and chives. Add cream as needed to adjust consistency; mixture should feel like stiff mashed potatoes. Season to taste with salt and pepper and reserve.
Cook sliced onion with butter very slowly in a pan over low heat until caramelized. Season with salt, pepper and chopped thyme and reserve.
Roll dough into 1/8-inch-thick sheets, then cut out 2-inch circles. Place a heaping tablespoon of filling onto each circle and fold into half-moon shape. Seal each pierogi with beaten egg.
Gently sauté 2 pierogies in olive oil. Top with onions and crème fraîche and serve.
Chris Santos, Chef-Partner, The Stanton Social, New York City