Thunder Cake: The Story, the Science, and the Recipe (Yes—With Tomatoes!)

I had completely forgotten about Thunder Cake—until our littlest little one casually announced one day that her kindergarten teacher’s son was planning to make one for her class. Just like that, the memory came rushing back. The book. The storms. The chocolate cake. And that one very unexpected ingredient.

Thunder Cake? That’s the chocolate cake made with tomatoes… right?

Before I knew it, memories of baking Thunder Cake (at least twice) with my oldest daughter back in her kindergarten or first-grade days started slipping in. So we decided to revisit it—baking Thunder Cake together and finally answering the big question:

Why on earth would anyone put tomatoes in a chocolate cake?

What Is Thunder Cake?

 

For those who’ve never met it before, Thunder Cake is a beloved children’s book by Patricia Polacco. The story follows a young girl who is terrified of thunderstorms and her wise grandmother, who helps her face that fear by baking a chocolate cake as the storm approaches.

 

As the thunderstorm rumbles closer, it's a race against time—gathering ingredients from the pantry and the garden—including the ripe tomatoes—before the storm hits. Baking together becomes a grounding, comforting ritual, turning fear into confidence.

 

The book famously includes the actual Thunder Cake recipe, which is why it’s so often used in classrooms—especially during spring units on weather safety, emotions, and coping skills.

 

And yet… even the most cake-loving kids pause at one ingredient: tomatoes. 

 

Why Are There Tomatoes in Thunder Cake?

No one knows for certain why Patricia Polacco chose tomatoes for her recipe, but there are a few solid (and fascinating) reasons it works.

1. Storytelling & Symbolism

In the book, the child must go outside to pick tomatoes as the storm approaches—forcing her to face the darkening sky and rising thunder. The tomatoes aren’t just an ingredient; they’re part of the emotional journey.

2. A Little Kitchen Science

Tomatoes are mildly acidic—similar (though gentler) than apple cider vinegar. Acid is often paired with baking soda in cakes to help them rise and create a lighter crumb. In that sense, tomatoes may function much like vinegar does in classic chocolate cake recipes.

3. Moisture Without Flavor

When peeled and fully puréed, tomatoes add moisture without adding a noticeable tomato taste. Think zucchini bread—but sneakier.

So… should you put tomatoes in a cake? Surprisingly, yes. When done right, they disappear completely.

Thunder Cake Taste Test: Will Kids Actually Eat It?

 

Short answer? Yes—usually.

 

If peeled, ripe tomatoes are fully puréed, there should be no clue that they’re in the cake at all. That said, our littlest one reported that the Thunder Cake she sampled elsewhere had visible bits of tomato skin still intact. She said it was good… after picking out all the tomato pieces. (Which tells me those tomatoes were definitely not puréed.)

 

At home, our girls helped make the cake from start to finish—including adding the tomatoes. The middle one was skeptical at first, but the promise of chocolate frosting won her over in the end. And once baked? No complaints. Just crumbs.

 

Tips for Making the Best Thunder Cake

• Peel and purée the tomatoes completely to avoid texture surprises
• Use red, ripe tomatoes. This gives maximum juicy moisture and minimal acidity
• Beat egg whites to stiff peaks—this step is key to the cake’s light texture
• Add tomatoes and water before folding in egg whites, so you can mix more confidently
• Don’t overbake—the goal is tender and airy, not dry

Thunder Cake Recipe (Inspired by Patricia Polacco's Book)

Ingredients

• 1 cup ripe tomatoes, peeled and puréed
• 1 cup water
• 2 cups all-purpose flour
• 1½ cups sugar
• ½ cup cocoa powder
• 1 tsp baking soda
• ½ tsp salt
• ½ cup butter, softened
• 4 eggs, separated
• 1 tsp vanilla extract

Directions

1. Preheat oven to 350°F (175°C). Grease and flour a 9x13-inch pan.
2. In a large bowl, cream butter and sugar until light and fluffy.
3. Beat in egg yolks one at a time, then add vanilla.
4. In a separate bowl, whisk flour, cocoa, baking soda, and salt.
5. Alternate adding dry ingredients with water and tomato purée to the batter.
6. In a clean bowl, beat egg whites to stiff peaks.
7. Gently fold egg whites into batter.
8. Pour into prepared pan and bake for 30–35 minutes, or until a toothpick comes out clean.
9. Cool completely and frost with your favorite chocolate frosting.

  

What Baking a Thunder Cake with the Kids Taught Me

 

Whether the tomatoes are there for science, symbolism, or story magic, the result is a surprisingly delicious chocolate cake—and a meaningful way to talk with kids about fear, courage, and weather safety.

Thunder Cake isn’t just a recipe. It’s a reminder that even the scariest moments are easier when your hands are busy, your heart feels safe, and there’s a promise of cake as an end reward.

 

And honestly? Any cake that helps kids face their fears—and sneaks in a fruit or vegetable—is a win in my book.