Preheat oven to 350. Spray an 8 square baking dish with cooking spray and line with parchment paper so the parchment extends over 2 sides of the pan. In a medium bowl whisk to combine flour, cocoa powder, SweetN Low, baking powder, baking soda, and salt. Add yogurt, water, applesauce, and vanilla and stir to combine. Scrape batter into prepared pan and bake until a toothpick inserted in the center comes out clean, about 25 minutes. Let cool completely in pan on a rack. In a medium bowl whisk to combine together cornstarch and SweetN Low. Whisk in yolks until smooth. In a small saucepan bring milk to a simmer. Slowly whisk about half the milk into yolk mixture, then whisk yolk mixture into remaining milk in saucepan. Place back on heat and, stirring constantly over low heat, cook just until thickened. Strain through a fine sieve into a medium bowl and stir in butter and peppermint extract. Press a piece of plastic wrap directly on surface of pastry cream and refrigerate until well chilled, at least 2 hours. In a medium bowl beat cream and SweetN Low with a hand mixer until softly whipped. Cut cake into ¾ cubes. Place a layer of cake cubes in bottom of each of 8 wide dessert cups or glasses. Top with a thin layer of peppermint cream, another layer of cake, and another layer of peppermint cream. Garnish each trifle with a spoonful of whipped cream and a sprinkle of peppermint candies. Save extra cake for another use.
