To make the cake:

1. Preheat the oven to 350°F. Grease and flour a 9 x 13 rectangular pan and set aside. Add the cake flour, baking powder, baking soda, and salt to a mixing bowl, whisk well to combine evenly, and set aside.
2. Beat the butter using a stand mixer and paddle attachment on high speed for 2 minutes until creamy. Scrape down the bowl and add the sugar. Beat for an additional 2 minutes, scraping down the bowl as necessary. Add the egg whites and beat on high speed for 2 more minutes, then add the sour cream and vanilla extract. Beat for one more minute, and scrape down the bowl one more time before adding the dry ingredients all at once.
3. Mix on low speed JUST until the flour mixture is incorporated, with maybe one or two flour streaks left. Turn the mixer back onto the lowest speed setting and stream in the buttermilk. Stop the mixer and use a spatula to gently finish mixing. You shouldn’t need more than two or three turn around the bowl.
4. Add the batter to the prepared 9 x 13 pan and bake in the preheated oven for 45 minutes. If you are serving this cake to slice, then only bake for 40 minutes. Allow the cake to cool completely before continuing with the recipe (~4 hours).

To make the frosting:

1. Beat the butter on medium high speed for about 2 minutes, using either a stand mixer or hand mixer. Scrape down the bowl.
2. Add the remaining ingredients and mix on low speed until blended, then beat on medium until very light, about 3 more minutes. Scrape down the bowl and beat for one more minute.

To assemble the cake pops:

1. Crumble the cake into the bowl of the stand mixer and use the paddle attachment to mix the cake into crumbles. Add one tablespoon of frosting at a time, and mix on low speed after each addition. Continue adding frosting this way until a good, packable consistency is reached. (If you’ve added too much frosting and the “dough” has now become a paste, see the above post for recommendations.)
2. Using a medium cookie scoop, pack and roll the mixture into balls, and place on a baking sheet lined with parchment. Refrigerate for at least 2 hours.
3. Melt about 1/4 cup of the white chocolate in a microwave safe bowl for 30 seconds on full power. Stir well to distribute the heat evenly and microwave again if necessary for an additional 10 seconds. Stir until the chocolate has melted completely.
4. Dip each treat stick into the small amount of melted white chocolate, just on the tip of one end. Press the coated end halfway down into a chilled cake ball. The chocolate will rise up a little further onto the stick and form a tiny button shape. Repeat for the remaining cake pops. Once every cake ball has a stick, allow the pops to chill in the fridge for 20 more minutes.
5. Working in batches of 5, dip each cake ball down into the white chocolate and allow it to come up and cover the button of chocolate that is already on the stick. Swirl the pop around in the chocolate to make sure that the entire ball is completely coated, and gently tap or twist the cake pop on the rim of the bowl to discard any excess. Add sprinkles immediately before the chocolate sets, so that they stick.
6. Push the empty end of each finished cake pop into the block of foam to dry. Repeat with the remaining cake pops. You may need multiple foam blocks, depending on how many cake pops you’re making.
7. Allow to chill and set in the fridge. Cake pops will be dry within a half hour.