It’s no secret that I have a soft spot for a cake made from a mix. I went into some detail about my love for boxed cakes here, but what I have not yet shared with you is my affection for a particular cake-mix cake — one that is no longer available, and one that I ate growing up (and by “growing up” I mean before, during, and after college). The cake in question was Betty Crocker’s Stir’n Frost and it appealed to me on a myriad of levels: It was an incredibly delicious fluffy, moist cake, with creamy sweet frosting (I was partial to the chocolate one with the vanilla icing). It came with its own pan, AND with a packet of frosting. You made the cake right in the pan by adding water to the mix and stirring (hence the name) and then frosted it with the packet once it emerged from the oven. Truth be told, I ate many a Stir’n Frost cake when it was still warm and the frosting kind of melty (umh, yum). This chocolate sheet cake with old-school buttercream frosting is my ode to the Stir’n Frost.
Funnily enough, and as is often the case, I did not actually set out to recreate the Stir’n Frost when I began developing this recipe for chocolate sheet cake. Quite to the contrary. The inspiration for this cake came at one of my many (okay, three) events for Icebox Cakes, when a woman in the audience raised her hand during the Q&A to tell me about her favorite chocolate cake recipe: The deluxe devils food cake recipe on the side of the Pillsbury Softasilk Enriched & Bleached Cake Flour box. I had been regaling the crowd with stories of my love of old recipes, particularly those from my collection of vintage recipe pamphlets, and she wanted to share her favorite old-school recipe, too. Of course, I immediately filed her’s away as a recipe that I needed to try (and by “try,” I mean analyze the recipe to determine what was special about it, what was not special about it, and what I could tweak to make it even more special). 
Analysis began almost immediately (yes, i move fast) and this is what I discovered: There was much overlap between the Softasilk recipe, my own extra moist and chocolate-y birthday cake recipe, and Barefoot Contessa’s Beatty’s chocolate Cake recipe, a superb chocolate cake that i’ve never actually made, but have eaten. Yes, there were some differences. Barefoot’s and Softasilk’s call for buttermilk as the liquid, and Barefoot’s and mine call for oil as the fat, but in the most general of ways, the proportion of ingredients to one another and the kind of ingredients matched up pretty closely. (All three cakes use about the same amount of flour, cocoa powder, sugar, and eggs.) Admittedly, my birthday cake uses a tad more sugar and eggs than the other two, but there’s no surprise there.
Long story short, as I began tweaking the Softasilk recipe (subbing some brown sugar for the granulated, adding a yolk, and some lightly whipped cream, among other things), thinking about what frosting I might ice my cake with (my old-school buttercream), and what shape I might bake it into (sheet cake), memories of the Stir’n Frost cakes of my childhood came flooding back. That’s when I knew this cake would be fluffy, not dense, with a thick layer of sweet and dreamy frosting. So, whether (like me) you remember Stir’n Frost cakes vividly, or (unlike me) have never had the pleasure of enjoying one, I promise this cake is for you.
Chocolate Sheet Cake With Pld-school Buttercream Frosting
Ingredients
For the cake
- 2 1/4 cup cake flour
- 1 cup dutch process cocoa powder
- 2 tsp baking soda
- 1 tsp baking powder
- 1 tsp salt
- 2 sticks of unsalted butter room temperature
- 1 1/2 cups light brown sugar
- 3/4 cup granulated sugar
- 2 tsp pure vanilla extract
- 1/2 tsp almond extract optional (see note below)
- 2 large eggs
- 1 yolk
- 1 1/2 cup buttermilk
- 3/4 cup heavy cream
For the frosting
- 3 sticks of unsalted butter room temperature
- 6 cups of confectioners' sugar sifted
- 1/2 to 3/4 cup of heavy cream room temperature
- 1 1/2 to 3 tsps vanilla extract or another flavoring, or to taste
- Scant 1/2 tsp salt
- A few drops of food coloring optional
Instructions
To make the cake
- Preheat the oven to 350 degrees. Spray a 13x9x2-inch pan, and line with parchment. Spray the parchment and set aside.
- iIn a large bowl, sift the flour, cocoa powder, baking soda, baking powder, and salt. Set aside.
- In the bowl of a stand mixer fitted with the paddle attachment, cream the butter on medium high speed until light and smooth. Add the two sugars, and the extracts and continue to beat on medium high speed, for 3 to 5 minutes, until the mixture is fluffy (full of air). Scrape the bowl down periodically.
- On medium speed, add the eggs and yolk, one at a time, waiting until each one is fully incorporated before adding the next one. Scrape the bowl as needed.
- Lower the speed on the mixer, and add the dry ingredients in 3 installments, alternating with the buttermilk, and beginning and ending with the dry. Begin with a bit more than 1/3 of the dry and scrape the bowl after the second installment of the dry. Stop the mixer when there is still a bit of visible flour in the batter and incorporate it by hand with a rubber spatula.
- Whip the cream in a separate medium sized bowl with a hand mixer until it holds soft peaks, or transfer the batter to a large bowl, and reuse the stand mixer's bowl after washing it. Fold the whipped cream in to the batter, gently.
- Transfer the batter to the pan and smooth the top with an offset spatula. Bake the cake for about 43 to 48 minutes, rotating at the midway point. Start checking the cake after 40 minutes — a cake tester should come out with a moist crumb or two, not clean (don't over bake). Let the cake cool to room temp before frosting.
To make the frosting
- Place the butter in the bowl of a stand mixer fitted with the paddle attachment and beat on low to medium-low until smooth. About 3 minutes. Begin adding the sugar, only a half cup at a time, keeping the mixer at the same speed. Once about 1/3 of the sugar is incorporated, stop the mixer and scrape the bowl with a rubber spatula. Return the mixer to the same speed, and add about 1/4 of the cream, mixing until incorporated.
- Continue slowly mixing in this fashion (adding sugar and cream, scraping with a spatula periodically, and taking time to let the mixer run in between additions), until most of the sugar and cream has been incorporated. Add the vanilla and salt, mix again and add the remaining sugar and cream. Continue mixing on medium-low (or lower) for at least 5 to 10 minutes, if not longer, adding the food coloring halfway through the mixing time, if you so desire. The frosting will be quite light, creamy, and fluffy when it is done. Store the frosting tightly covered at room temperature for up to 24 hours or refrigerate it for up to one month. Bring the frosting to room temperature prior to using.