Strawberry Roll Cake

 The Art.

    Happy Valentine's Day, everyone! I know I've been gone awhile, but I had to come out of my baking hiatus to bring you a Valentine's Day treat because I think we all could use a little extra love right now. Inspired by the Japanese roll cakes all over the internet with cute designs baked into the sponge, I wanted to make a beautiful Valentine-themed roll cake with hearts on the outside. Not only did I want the outside of the cake to be pretty, but I wanted to create a cake where there was a perfect spiral of beautiful strawberries in every slice. This is where the internet failed me-- most of the roll cakes with strawberries in the center were either whole berries that didn't allow the cake to have a tight, pretty roll, or randomly sliced fragments. My engineer husband and I put our heads together and created the foolproof way to make a show-stopping cake with a perfect strawberry pattern running all the way through! What could be a more romantic way to celebrate Valentine's Day than solving a dessert engineering puzzle?

The Science.

    So, how did we engineer these perfect strawberry spirals, you ask? It begins with understanding that each slice of the roll cake is a cross-section of the strawberries inside. The problem is, strawberries are not the same diameter from top to bottom. They have a lovely heart shape that we all enjoy, but for our roll cake that is a problem. This is why I cut off the bottom point of all the strawberries and stacked them all end-to-end across the cake for long, even rows strawberries throughout.  I also decided that we needed to half the strawberries so that when we rolled the cake they would follow the contours of the roll and generate a lovely spiral. 

    The cake itself is a beautiful sponge that is full of whipped eggs to make it light and airy, but also gives the cake enough strength to roll without falling apart. There are three baking tools that I use here that I think are absolutely necessary for success: a proper jelly roll-sized pan, a silicone baking mat, and a heart-shaped cookie cutter.

The Recipe:

Cake:

4 large eggs, separated

1/2 cup granulated sugar, divided

1 teaspoon vanilla

1/4 teaspoon salt

1/4 cup all-purpose flour

1/4 cup cornstarch

powdered sugar

Filling:

1 cup heavy whipping cream

1/4 teaspoon gelatin

1 lb fresh strawberries

    Preheat your oven to 350°F and place rack in the middle position. In a large bowl, beat together the egg yolks, 1/4 cup sugar, and vanilla with an electric mixer until pale yellow and fluffy. Set aside. In another clean bowl with clean beaters, whip up the egg whites with the salt until soft peaks form. Gradually add in the remaining 1/4 cup sugar to the egg whites and continue beating until stiff peaks form. Set aside. Sift the flour and cornstarch into the egg yolk mixture and gently fold in with a spatula. 

    If you are making heart designs on the outside of your cake, this is where you will want to remove a few tablespoons of the batter and dye it. I used Wilton's Gel Icing Colors in No-Taste Red because it gives a lovely strawberry-red color and it doesn't impart a bitter flavor like other dyes. Line your jelly roll pan with the silicon mat. To make a perfect grid of hearts, I dipped my heart cookie cutter in the red batter and used it as a stencil to make hearts on my silicone mat. I also used a ruler to get perfect spacing, then I used a spoon to fill the hearts in with the batter.

My cookie cutter is 1.5 inches wide and I spaced my hearts 2 inches apart, but you can do any pattern you wish! Just remember that you will be trimming off 1/2 inch on the ends once the cake is rolled. Place your designs in the freezer for 20 minutes.

    While freezing your designs, complete the sponge batter by folding in the egg whites--first stirring in 1/3 of the egg whites to lighten, then gently folding in all the egg whites with a spatula until just combined. If you fold the egg whites in before you complete your heart designs, then the batter will deflate by the time you want to spread it into your jelly roll pan. Take your pan out of the freezer and gently plop dollops of your batter all over. This will minimize the amount of spreading you have to do and prevent messing up your heart pattern. Even out the top of the cake with a spatula ever-so-gently, going all the way to the corners and the edges. Place in the oven and bake for 12 minutes, or until the cake is very light golden and springs back when you touch it lightly. 

    Cool the cake in the pan for 10 minutes, until slightly warm. Run a sharp knife along all the edges and sift a layer of powdered sugar on top, then cover with a piece of parchment paper. Begin rolling up the warm cake from the short side, rolling up the parchment paper and the silicone mat right along with the cake. Once the cake is rolled, place it on the countertop with the seam edge on the bottom. Support the long sides of the cake with a rolling pin, baking pan, storage jar, or any other long object you have in your kitchen, in order to prevent the roll from sagging while it cools. Meanwhile, make the stabilized whipped cream following the recipe from my Chocolate Roll Cake and slice up your strawberries as in the photos.

Assembly:

    Gently unroll the cake and remove the parchment paper from the top, leaving the cake on the silicone mat. Spread the whipped cream evenly over the top of the cake, leaving one inch bare on all the edges. Next, make 4 rows of strawberries spanning the short length of the cake, cut side up as shown. 

(I may or may not have rolled it up with the strawberries the wrong way and had to unroll it and try again, which explains why the photo is so messy. This is the kind of R&D that I do for all of you so you can get it on the first try.) 

    Begin rolling up the cake from the short end, the same direction you rolled it before. As you start rolling, gently pull the silicone mat up and away from the cake with one hand as you form a tight cake roll with the other. Using the mat in this way supports the cake and helps you roll it more tightly. You want to roll the cake so that the center has a nice swirl, but not so tight that you squeeze your strawberries out. Going slowly and keeping the mat taught will make this easier.

    Once the cake is rolled, place it with the seam edge down on a cake board or serving dish. Cover
with parchment paper and support the long sides once again to keep a round shape. Refrigerate for at least one hour. Before serving, remove the parchment paper and trim off the short ends of the cake (approximately 1/2 inch) with a sharp serrated knife to reveal a beautiful swirl of strawberries.

    I have to say I was so pleased with how the strawberries looked inside the cake. We had family over and every single slice I cut had four perfect strawberry slices in it, all the way to the end. If you have any left, you can store leftover cake in an airtight container in the refrigerator for up to two days.