For cake, preheat oven to 350℉. Butter and flour two 8” cake pans and line bottoms with parchment paper.
In a medium bowl, whisk together flour, baking powder, and salt. In a large bowl or the bowl of a stand mixer fitted with the paddle attachment beat butter, sugar, and Stevia In The Raw® until light and fluffy, 4-5 minutes. Beat in eggs 1 at a time, scraping down bowl and beaters after each addition. Beat in vanilla. Stir in flour mixture until just combined.
Divide batter evenly between cake pans. Smooth tops and bake, rotating pans halfway through baking, until a toothpick inserted in the center comes out clean, 30-35 minutes. Let cool in pans on a rack for 10 minutes, then unmold onto rack to cool completely.
For cranberry-orange sauce, in a large saucepan combine sugar, Stevia In The Raw®, and 2 cups water. Bring to a boil and boil 5 minutes. Add cranberries and orange zest and reduce heat to simmer gently until berries are translucent, about 5 minutes. Transfer to a bowl to cool completely.
For vanilla custard, in a medium bowl whisk together sugar, Stevia In The Raw®, cornstarch, egg yolks, egg, and salt. In a medium saucepan bring milk to a simmer. Whisking constantly, pour half the milk into the egg mixture. Pour egg mixture, whisking constantly, back into saucepan with remaining milk. Cook, stirring constantly, over medium-low, until mixture thickens, about 2 minutes. Scrape custard into a bowl and stir in vanilla. Place a piece of plastic wrap directly on the surface of custard, and chill until cold, at least 2 hours.
For cranberries, in a medium bowl toss cranberries with egg white to lightly coat. Roll cranberries in sugar, then spread out in a single layer on a baking sheet and let dry for 2 hours at room temperature.
When ready to assemble trifle, make whipped cream. In a large bowl or the bowl of a stand mixer fitted with the whisk, beat cream, Stevia In The Raw®, and vanilla on medium speed until stiff. Beat custard in a medium bowl until creamy.
To assemble, cut cakes into 1” chunks. Scatter half the cake cubes in a 2-3 quart serving bowl (preferably glass, to see the layers). Spread half the cranberry sauce on top. Top with half the custard. Top with remaining cake cubes, then cranberry sauce, then custard. Spread whipped cream evenly on top, and decorate with frosted cranberries and orange zest.