Preheat oven to 325

Lightly grease a 9x13 baking dish

Dump dry cake mix and pudding mix in a mound in prepared baking dish. Make a well in the center of dry ingredients

Combine reserved juice from mandarin oranges with enough orange juice to measure 1 1/2 cups liquid. Add eggs and juice mixture to well and whisk together until well-blended, scraping down sides

Stir in mandarin oranges and spread batter evenly in dish

Arrange butter slices over the top. Sprinkle with cookie crumbs

Bake about 45 minutes. Cool completely

Optionally, spread whipped topping over cake before serving