Candy Bar Sheet Cake

Heat the oven to 325 degrees. Grease a 9-by-13-by-2½-inch metal baking pan with baking spray.

In a large bowl, whisk together the flour, milk powder, cornstarch, baking powder and salt. In a medium bowl, whisk together the sugar, whole milk, oil, vanilla and egg whites until smooth. Pour the liquid ingredients over the dry ingredients and whisk until just combined. Pour the batter into the prepared pan and smooth the top. Bake until pale golden brown on top and a toothpick inserted in the center of the cake comes out clean, about 40 minutes.

While the cake is in the oven, make the butterscotch sauce: Combine the brown sugar, whole milk, butter and salt in a small saucepan and melt over low heat. Increase the heat to medium and cook, stirring often, until the sauce thickens, about 8 minutes. Remove the pan from the heat and stir in the sweetened condensed milk and vanilla. Pour the sauce into a bowl and let cool to room temperature or refrigerate until no longer warm.

Remove the cake from the oven and transfer to a wire rack. Let the cake cool for 20 minutes, then use a 1/2-inch-wide wooden dowel or handle end of a wooden spoon to gently poke holes three-quarters of the way down the cake and spaced about 1 inch apart. Pour the butterscotch sauce all over the cake, aiming to get most of it to soak into the holes in the cake.

In a large bowl, whisk the cream by hand or with a hand mixer until stiff peaks form. Scrape the whipped cream onto the cake and use a small offset spatula or table knife to spread it evenly over the top. Sprinkle the chopped candy bars all over the cake and chill in the refrigerator for 1 hour before serving from the pan.