First make the oleo sacchrum. In a small container, add sugar and orange peels. Use the back of a spatula or a muddler to mash the peels into the sugar for 1-2 minutes or until the sugar starts to look wet. Cover and let it sit for 4-5 hours, mixing often. When it’s done, the sugar should be slightly translucent and syrupy. Transfer the oleo sacchrum to a large mixing bowl and add the milk, heavy cream, evaporated milk, sweetened condensed milk, and clear vanilla extract. Stir well, making sure all the sugar is dissolved. Strain the mixture into a large measuring cup and refrigerate. 

Preheat the oven to 350°F and lightly grease a 9×13 cake pan with cooking spray or butter. Set aside.

In a large mixing bowl, add cake mix, eggs, milk, melted butter, clear vanilla extract and kosher salt. Whisk until you have a smooth batter and pour into the prepared baking pan. Bake for 23-25 minutes or until a toothpick inserted in the center comes out clean. Cool the cake for 30 minutes. Use a fork to poke holes all the way to the bottom of the cake every 1-2 inches across the entire surface. Stir the milk mixture and then pour it over the cake. Let the cake rest for 10-15 minutes so that the cake soaks up all the milk. Cover the pan with plastic wrap and place in the fridge for 1-2 hours. 

To make the whipped cream, add whipped cream, powdered sugar, and clear vanilla extract to a large mixing bowl. Whisk for 4 to 5 minutes, or until you have semi-stiff peaks. Spoon the whipped cream onto the chilled cake and spread into an even layer. Top with orange slices and chill until ready to serve.