Everyone in my family has a preferred birthday cake — naturally — and they never really change. My sister’s? Funfetti cake, as in Funfetti from the Pillsbury box. My Dad’s? Fruit cocktail cake: box yellow cake mix with canned fruit cocktail mixed in and Cool Whip on top (which I might also make a version of some time.) Mine? This. Of course, I don’t make it easy on anyone, including myself. My mom’s birthday is coming up at the end of September, and every year, she makes (or we make for her) what has always just been called “picnic cake”.
It’s yellow cake from a box mix, with chocolate chips and marshmallows scattered on top, then baked. For a my whole life, I just thought “picnic cake” was simply *this* cake, but come to find out it loosely refers to any single-layer cake that is baked and frosted in the same tin, and can easily be transported and served to many people at, let’s say, a picnic!
“This was a cake my mom made for us,” my mom explained to me over text, noting that because the marshmallows toast on top, you don’t have to frost it. “One layer. Not messy. This would become my birthday cake every year growing up and grown!” She says that a traditional picnic cake is a yellow cake with thick chocolate icing, but I can’t find much information otherwise about picnic cakes online, and everyone seems to have their own version of one. Shockingly, my mom and I haven’t come across anyone who does picnic cake quite like this, and we’re not really sure where my grandma got the inspiration, if anywhere. If you know of more resources about picnic cakes or have your own picnic cake recipe, I would love to hear about it! [Note: After posting about this on TikTok and Instagram, a small few people have come forward saying that they’ve also tried this cake at family events. One said their grandma got it from a magazine in the 60s. Others still mentioned variations like s’mores cake, dump cakes, or other picnic cakes like “beer-box cakes“.]
I wanted to make an EGO version of this formative dessert that was just one step up from box mix. (Although I don’t know if my family will accept it for my mom’s birthdays going forward.) But also, store bought really is fine sometimes, so if you want to follow my mom’s directions for box mix, do it! Here they are, word for word:
Make yellow cake mix as directed. Pour into 9×13 pan. On top of batter, drop choc chips, 3/4 bag. Cover chips with bag mini marshmallows. Press lightly. Bake as directed on box.
In this version, we’re using the reverse creaming method where dry ingredients are mixed with softened butter before adding liquids. This is instead of the traditional creaming method where butter and sugar are beaten together, then the eggs are added, and then alternating the wet and dry ingredients. The reverse creaming method attempts to prevent excess gluten development by coating the flour pieces in butter, resulting in a cake that is more tender, has a more even structure, and bakes up flatter.
I also found that, due to this cake having a lot of liquid and eggs, it didn’t bake as fast under the blanket of marshmallows. So by the time the center cooked, the edges overcooked and the marshmallows evaporated or went a little past toasty. That’s why we’re adding the marshmallows toward the end of baking. This means the cake’s structure can set up, the water can evaporate from the batter, and the marshmallows don’t over-cook. I use a 9×13 pan that’s a little over 2 inches deep. I know some of the glass Pyrex ones are more shallow, so be sure to only fill the pan about halfway. Otherwise, you could have some overflowing marshmallows. (We put a tray underneath just in case to catch any spillage.)
This is not the prettiest cake in the whole world, but it is super portable, very unique and a little retro. The marshmallows get toasty and sticky, and almost seep into the top of the cake, keeping it really moist. Despite the pictures, the chocolate chips actually don’t all sink to the bottom. (With the box mix version they usually do, and that’s how my family likes it!) It’s so fluffy and bright yellow thanks to its use of four large eggs. And with lots of vanilla and buttermilk, it is reminiscent of that nostalgic box mix, but also feels pretty luxurious.
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