Chocolate Toffee Crunch Cake

Back in 2019 I made bi-monthly birthday cakes for the office. This post has a link to the 6 cakes I made that year, which were an Orange Dream Cake, Verry Berry Cake, Triple Chocolate Cake, German Chocolate Cake, Lemon chiffon cake with fruit and lavender pastry cream, and an Apple spice cake with salted caramel cream cheese frosting. 

I've made some treats periodically since then, but not as many as I'd like (you know, Covid and all). And this past year (2022) was a lot busier, so I didn't have an opportunity to make an office birthday cake until October. But man, did I make up for lost time with this chocolate toffee crunch cake. 

Yup. You heard that right. Chocolate. Toffee. Crunch cake.

I actually ended up making two cakes because I was afraid one wouldn't be enough. And I'm glad I did, because folks ended up going for seconds!

That homemade toffee in each layer is what took this from a delicious chocolate cake to an exquisite chocolate cake. If you take nothing else from this post of mine, it's that you need to make toffee, crush it up, and add it to your cake filling!

And that chocolate swiss meringue buttercream was not only addictive, it was an absolute dream to pipe. Plus it was fun playing around with my piping tips again after all this time!

For the first of my two cakes I copied the style from The Cake Blog post, with a bit of a sweater aesthetic that was fun to do. Check out that post for even more pretty pictures of her cake.

For my second cake I went a bit more abstract, piping different florets and squiggles.

It wasn't just a pretty cake on the outside either. Look how awesome the cake looked when sliced up!

Yours in always trying new cake recipes,
Jacqueline

Chocolate Toffee Crunch Cake, adapted from The Cake Blog (cake, frosting, and assembly), Serious Eats (frosting), and Handle the Heat (homemade toffee).

Note: The original recipe calls for cinnamon in the cake and simple syrup. I wasn't sure how I'd like it so I only added cinnamon to the cake and not the simple syrup. In the end I actually was not a fan of the cinnamon/chocolate cake combination, but so many people like it that I'll include it in the cake recipe below. But if I were to make this again, I'd amp up the coffee flavors (for a mocha toffee take) and get rid of all traces of cinnamon. :)

If you want to split this recipe up over a few days, this is what I did:
* Day 1: Make cake. Make toffee. 
* Day 2: Make frosting. Make simple syrup. Assemble cake (refrigerate). Decorate cake.
* Day 3: Serve cake (allow it to come to room temperature before serving).

I use Diamond Crystal kosher salt. Use about half as much if using table salt or Morton's (see this post with a conversion chart if using another kind of salt).

Ingredients

Cake
1 ½ cup coffee (or water)
¾ cup unsalted butter
½ cup (~50 g) unsweetened Dutch-processed cocoa powder 
3 large eggs
¾ cup buttermilk
2 TBSP canola oil
2 tsp vanilla extract
3 cups (375 g) all-purpose flour
2 cups (400 g) granulated sugar
1 ½ tsp baking soda
½ tsp baking powder
1 tsp kosher salt 
1 tsp cinnamon (optional; see note above)

Chocolate swiss meringue buttercream
170 g egg whites (6 oz; 2/3 cup), from 5 to 6 large eggs
325 g sugar (11.5 oz; ~1 2/3 cups)
¼ tsp cream of tartar
1 tsp kosher salt
24 ounces unsalted butter (6 sticks), softened to 65°F Note: you can reduce to 16 oz butter if you feel that is enough when you are making the frosting
2 tsp (5g) vanilla extract
6 ounces (170 g) dark chocolate, chopped Note: Chocolate chips can also be used without issues. Feel free to increase the chocolate up to 14 oz (400 g) if you want a more chocolately frosting
1 teaspoon instant espresso powder (optional), dissolved in a few drops of hot water 

Homemade Toffee 
4 oz (half stick) unsalted American butter
½ cup (100 g) brown sugar
½ tsp kosher salt

Simple syrup
½ cup granulated sugar
½ cup water

Directions

1. PREPARE CAKE: Preheat the oven to 350°F. Grease three 8-inch round pans, insert parchment round on the bottom, and re-grease and flour the pans. Set aside.
2. Place coffee, butter, and cocoa in a saucepan over medium-low heat. Stir to combine and remove from the heat once butter has melted.
3. Meanwhile, in a medium bowl stir together eggs, buttermilk, oil, and vanilla. Set aside.
4. In a large mixing bowl or bowl of a stand mixer, whisk together flour, sugar, baking soda, baking powder, salt, and cinnamon (if using). 
5. Add the cocoa/butter mixture and stir to combine. Add the buttermilk mixture and whisk until batter is smooth.
6. Evenly distribute cake batter into prepared cake pans. Bake for 30 to 35 minutes, or until a toothpick inserted into the center of the cakes comes out clean.
7. Cool the cake on a wire rack for 15 to 20 minutes before removing the cakes from their pans. Cool completely before filling and frosting. (If assembling the next day, wrap cakes in plastic wrap and leave on the counter.)
   
   
8. PREPARE TOFFEE: Line baking sheet with parchment paper or a silicone baking mat. Set aside, along with an offset spatula. (Check out the post from Handle the Heat if you want pictures of this process.)
9. In a heavy bottomed small saucepan, melt butter over medium heat. Add sugar and salt and whisk vigorously for one minute until combined. Cook, stirring constantly, until mixture looks like melted peanut butter and is between 295 and 305°F, about 10 minutes. (If the mixture separates, remove from heat and whisk vigorously until recombined. Return to heat and continue cooking.)
10. Immediately and carefully pour the hot toffee onto the prepared baking pan, spreading it into an even layer. Let cool and harden for about 20 minutes.
11. Place the sheet of toffee on a cutting board or in a zip top bag. Use a mallet, rolling pin, or heavy object to crack it into small pieces. You can also cut into bits with a sharp serrated knife. Store in an airtight container for up to 1 week.
    
    
12. PREPARE BUTTERCREAM: Add egg whites, sugar, cream of tartar, and salt in bowl of a stand mixer and whisk gently by hand until combined. Place mixing bowl over a pan of simmering water to create a double-boiler. Whisking gently but constantly, heat the egg mixture until it registers 160°F. 
13. Using the whisk attachment, whip the egg mixture on high for 8 to 10 minutes until stiff, glossy peaks and the outside of the mixing bowl returns to room temperature. Put the bowl in your refrigerator for 5 to 10 minutes (or longer) if the mixture is still too warm. You want the meringue to be around 90°F before proceeding.
14. Switch to the paddle attachment. With the mixer on low, slowly add butter (a couple tablespoons at a time) and mix until incorporated. 
15. Meanwhile, melt chocolate until warm (either in microwave using 10- to 15-second bursts, or water bath) and set aside. 
16. Once butter has been incorporated into the frosting, add vanilla. Mix on medium until silky smooth, about 3 to 5 minutes. Add in the melted chocolate and dissolved espresso powder and mix on medium until smooth.
    
    
17. PREPARE SIMPLE SYRUP: Place sugar and water in small saucepan and bring to simmer over medium heat. Stir until sugar is dissolved. Remove from heat and set aside. 
    
    
18. ASSEMBLE THE CAKE: If cake layers have domed, use a large serrated knife to level the cake (snacking on the extra cake or turning it into cake pops). Brush the cake layers with warm simple syrup (gently reheat in the microwave, if needed). Note: I didn't use all the simple syrup and saved the remaining syrup for my morning coffee.
19. Place the bottom layer of cake on a cake board or serving dish. Dollop ¾ cup of buttercream and spread with an offset spatula. Sprinkle on a generous amount of toffee bits (about 1⁄3 cup) and gently press into the buttercream. Add a small amount of buttercream on top (about ¼ cup) and spread to secure the toffee bits. Place the next layer of cake on top and repeat.
20. For the final layer, place the cake upside down so that the bottom, smooth edges of the cake are facing up.
21. Smoothly frost and decorate with the remaining frosting. Use star and round piping tips to create different patterns on the sides of the cake. If you don't feel comfortable with piping, here's a simple technique using blobs of frosting and a spoon to create a gorgeous pattern!