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5 from 6 votes

Strawberry Sheet Cake with Rhubarb Swiss Meringue Frosting

Strawberry Sheet Cake with Rhubarb Frosting is a fluffy strawberry-flavored cake for a crowd topped with the most delicious roasted swiss meringue that tastes like rhubarb.
Prep Time30 mins
Cook Time35 mins
Total Time1 hr 5 mins
Course: Brunch, Dessert
Cuisine: American, English
Keyword: carrot sheet cake, rhubarb, roasted rhubarb, sheet cake with strawberries, strawberry cake, strawberry sheet cake, strawberry shortcake, strawberry shortcake sheet cake
Servings: 1 sheet cake
Calories: 302kcal
Author: Adrianna Adarme
Cost: $15

Ingredients

Roasted Strawberries + Rhubarb:

  • 2 cups sliced strawberries from 1/2 pound strawberries
  • 1/4 cup white granulated sugar divided
  • 1 cup diced rhubarb from 4 to 5 shortish stalks
  • Pinch of salt
  • 3 drops of red food coloring optional

Strawberry Sheet Cake:

  • 2 3/4 cup cake flour plus more for dusting pans
  • 2 1/2 teaspoons baking powder
  • 1 teaspoon salt
  • 1 cups unsalted butter
  • 1 3/4 cups white granulated sugar
  • 3/4 cup milk
  • 6 large egg whites
  • 2 teaspoons pure vanilla extract or 1/4 teaspoon vanilla paste

Rhubarb Swiss Meringue Frosting:

  • 3 large egg whites
  • 3/4 cup white granulated sugar
  • 1 cup unsalted butter at room temperature
  • 1/4 cup rhubarb puree
  • 2 to 3 drops of red food coloring optional

Instructions

To Make the Roasted Strawberries + Rhubarb:

  • Preheat the oven to 350 degrees F. Add the sliced strawberries to one side of a parchment-lined baking sheet and the diced rhubarb to the other side. Sprinkle about 2 tablespoons of sugar onto the strawberries and sprinkle the remaining 2 tablespoons of sugar onto the rhubarb. Toss them gently and keeping them separate, transfer them to the oven to roast for 10 minutes.
  • Remove and allow them to cool for about 5 to 10 minutes. Add the strawberries to a blender and pulse until smooth. (You should end up with about 1/2 cup puree. Mix in 3 drops of food coloring, if you like.) Next, add the rhubarb to the blender and pulse until smooth.

To Make the Sheet Cake:

  • Keep the oven at 350 degrees F (as it was for roasting the strawberries). And grease a 13x9-inch baking pan. Set aside.
  • In a medium bowl, add the cake flour, baking powder and salt. Whisk until combined. Set aside.
  • To the bowl of a stand-up mixer with the paddle attachment, add the butter and sugar. Beat until light and fluffy, about 2 to 3 minutes. In a measuring cup, pour in the milk, egg whites, vanilla extract or paste and reserved 1/2 cup strawberry puree (discard any extra) and whisk until combined.
  • Turn the mixer to low speed and, alternating between the dry ingredients and the liquid ingredients (the strawberry/egg white mixture), add the them butter/sugar mixture until the batter is relatively smooth.
  • Pour the batter into the prepared baking pan and transfer to the oven to bake for 25 minutes, until a skewer inserted into the center comes out clean.
  • Allow the cake to cool in the pan for about 5 minutes and then invert onto a cooling rack and cool to room temperature. It’ll probably take a good hour.

To make the frosting:

  • Bring a saucepan filled with a few inches of water. Place the clean bowl of a stand-up mixer atop the saucepan. Add the sugar and egg whites to the bowl and mix.
  • Heat the mixture until it reaches 140 degrees F or until the sugar has dissolved completely. Carefully (it’ll be hot!) transfer the bowl to the stand-up mixer and with the whisk attachment, beat for 5 to 7 minutes, until very fluffy. Remove the whisk attachment and replace with the paddle attachment. With the mixer running on low speed, add the butter, one cube at a time until smooth and glossy. Lastly, pour in the rhubarb puree and red food coloring and mix until combined.

To Decorate the Cake:

  • When the cake is completely cool, pour the frosting on top of the cake. Using an offset spatula or any spatula you own, smooth it out until it reaches the edges. Make a few swoops in the frosting so it looks cute. And then top it with a bunch of sprinkles!

Notes

Some Swiss Meringue Assistance:
When you add the puree, the frosting may curdle a bit. Here's how to fix it:
Remove 1/4 cup (you can eyeball this measurement) of the frosting and microwave it for about 30 seconds OR set it over a double-boiler until it's very smooth and melted.
With the mixer running, slowly pour in the melted frosting. Beat for an additional two minutes. The frosting will magically come together and become fluffy and cohesive!
If you're frosting is soupy, stick it in the fridge for about 5 to 10 minutes and then beat it for 1 to 2 minutes. It should stiffen up a bit.
If rhubarb is out of season, you can replace it with strawberry puree. I would double the amount of strawberries and then use the exact same measurement of puree for the frosting (1/4 cup of strawberry puree).