For the cake:

1. Butter a sheet pan with sides (jelly roll pan), and set aside.
2. Preheat oven to 350 degrees F.
3. Pour the cake mix into a large mixing bowl.
4. Strain the orange juice to remove big chunks.
5. Add the orange juice, orange zest, eggs, and melted butter to the bowl.
6. Mix together with a whisk until light and creamy, about 2 minutes. Pour into buttered pan, and use a spatula to spread it out. The consistency is a little different than a normal cake mix, so you need to be sure to spread the batter to the edges; it won't go there on its own.
7. Bake for 17 to 20 minutes, or until the top is lightly golden and the cake springs back when touched.
8. While the cake is baking, make the icing.

For the orange vanilla bean icing:

1. In a medium bowl, whisk together the butter, orange juice (unstrained -- the pulp is pretty), orange zest, and vanilla bean paste.
2. Add 1 cup of powdered sugar, and whisk it all together until you get a smooth wet paste. This is the time to get all of the lumps out.
3. Add the powdered sugar, one cup at a time, whisking after each cup, until you get a soft icing consistency, around 3 1/2 cups of powdered sugar. The icing should be thin, but not run off of a spoon dipped into it. Ice the sheet cake in the pan after it has cooled completely.
4. Garnish with orange candy slices if you'd like.