Preheat the oven to 350 degrees F.
For the cake: In a large bowl, combine the cake mix, pudding mix, buttermilk, oil, eggs, lemon zest and lemon and lime juices. Whisk well, or beat with a hand mixer, until the batter is combined and smooth.
Pour the batter into a 9-by-13-inch nonstick baking pan, or use a regular pan coated with cooking spray. Bake until the cake is baked through, 25 to 30 minutes. Remove the cake from the oven.
For the glaze: Combine the powdered sugar, butter, buttermilk, lemon and lime zests and lemon juice in a saucepan and whisk well to combine. Bring the mixture to a simmer over low heat. Remove from the heat.
Slice the cake into even pieces and drizzle the glaze over the top.
This recipe was created by a contestant during a cooking competition. The Food Network Kitchens have not tested it for home use, therefore, we cannot make any representation as to the results.