Step 1

Preheat the oven to 350 F and heavily grease a 9-by-13-inch cake pan with cooking spray.

Step 2

In a large bowl, sift the flour, baking soda, baking powder and salt. Set aside.

Step 3

In the bowl of a stand mixer fitted with the paddle attachment, add the sugar and citrus zest and mix on medium speed for about 30 seconds, or until the citrus zest becomes fragrant.

Step 4

With the mixer running on low, add the butter, 1 tablespoon at a time. Raise the speed to medium and cream the butter and sugar together until fluffy, about 2 minutes.

Step 5

Scrape the sides and bottom of the mixing bowl with a rubber spatula and add the vanilla extract. Mix again for about 30 seconds.

Step 6

Add the eggs, one at a time, mixing for about 15 seconds after each addition, being careful not to overmix.

Step 7

In a small bowl, whisk together the buttermilk and sour cream.

Step 8

Add the dry ingredients in thirds, alternating with the buttermilk mixture, mixing for about 15 seconds after each addition. Scrape down the sides and bottom of the mixing bowl and mix on medium speed for 20 seconds once all ingredients are added.

Step 9

Pour the cake batter into the prepared dish. Bake for about 35 minutes, or until a tester inserted into the center of the cake comes out clean.

Step 10

Using the bottom of a spoon or another small round-ended utensil, poke holes in the cake, about 1- inch apart. Brush the citrus juice across the cake with a pastry brush.

Step 11

While the cake continues to cool, whisk the pudding mix and milk together in a medium bowl until combined. Pour the pudding mixture over the cake.

Step 12

Top with whipped cream and citrus zest. Cover and allow to chill in the refrigerator for at least 3 hours before serving.