On Baking and Math (plus a chocolate-coffee-caramel cake to die for)

Have any of you read How to Bake Pi, by Eugenia Cheng? It’s a fantastic book, if you’re a fan of mathematics. Or baking. Or both, if you’re like me.

I’ve been thinking about math and baking a lot recently. Do you know those problems you used to get in elementary school? If 5 men can build a wall in 5 hours, how long does it take 12 men to build a wall two twice as long? I encountered one of those with baking a few weeks ago, when I did my Elmo test cake. I know the Wilton cake chart estimates something like 24 slices for a 9″ cake, but I thought for most birthday parties people would prefer a slightly larger slice. So my problem went something like this: if 6 people eat 3/4 of a one-layer 9″ cake, then how many people can eat a full two-layer 9″ cake? The answer, if we assume everyone eats the same volume of cake, is 16 (you can check my math and correct me if I’m wrong!).

Today, it was more fractions. I made a mistake with my buttercream today – I thought I’d measured out too little powdered sugar, but when I added more, my buttercream turned into a giant lump! So I weighed my buttercream, figured out the weight of my sugar, then added the right amount of butter to get the butter and sugar ratios to work out. Voila! My buttercream was saved! And all it took was a kitchen scale and a bit of math.

For those of you who are more interested in baking than in numbers, all of my cake information is below:

I decided to try a new chocolate cake recipe, one made specifically for a 6″ cake pan (I’ve so far been adapting an 8″ cake recipe). This chocolate cake recipe turned out fantastically! Though I only have one 6″ pan, so it was harder to tell that my ratios were even when I divided the batter – I ended up with 2/3 in one oan and 1/3 in the other, so I settled on a three-layer cake to even everything out.

I had to do a bit of research for this cake, because I wasn’t sure if it was a good idea to let the remaining batter sit while one layer baked; I’ve always been told that baked goods with baking soda should be baked right away. But, in one baker’s experience, chocolate cake batter rested well in the fridge, so I popped my remaining batter in the fridge and hoped for the best. The two cakes looked practically identical (with perhaps a little less rise in the second layer after sitting for 30-40 minutes in the fridge), so luckily this was a successful experiment.

I decided on a coffee and caramel cake, so I drizzled my cake layers in a sugar syrup with half water and half coffee, to add some moisture and extra coffee flavour to the cake.


For decorating, I divided my buttercream and made three flavours. One was plain vanilla, one was caramel-chocolate (made by mixing in melted baker’s chocolate with dulce de leche), and the last was coffee-chocolate (made by mixing in melted baker’s chocolate and cold coffee).

I used the vanilla buttercream in between cake layers, on top, and for the crumb coat. On the bottom layer, I opted a ring of buttercream and filled the center with dulce de leche. For the second layer, I filled with, for lack of a better word, coffee goo. I made this by mixing milk, coffee, sugar, and cornstarch on a stove top until the mixture thickened. Then once it was cool I spooned it onto the second cake layer.

I’ve been meaning to try a rosette pattern on a cake, so I did a two-layer ombre with the coffee and caramel buttercream. I slightly underestimated the amount of buttercream I needed, so there are a few less pretty rosettes on one side of the cake, but since this is just for me and my boyfriend, I’m not too concerned about a little mess up (OK I’ll admit it bothers me, but I just ate that slice first so now I can pretend that it never happened).


To finish off the cake, I grated some chocolate curls and piled them in the center. I was hoping to add a coffee bean or two, but unfortunately we didn’t have any whole bean coffee on hand.


I couldn’t resist trying a piece right away. There are so many amazing flavours here: the chocolate, caramel, coffee, and vanilla blend wonderfully with every bite, and the syrup makes for a delightfully most cake.


In future, I’ll be sure to make a bigger batch of buttercream to finish off the rosettes, but I don’t think I’d change anything else about this cake. In terms of flavour, it’s my favorite creation so far.

EDIT: Maybe it’s the scientist in me, but I believe in citing my sources, and I totally forgot to link to the chocolate cake recipe I used. I know some people spend forever tweaking a recipe to be just right, so I want to give credit where credit is due (plus it’s a fantastic recipe and I highly recommend it if you’re looking to make a dainty 6″ cake. It’s super light but still has a great chocolate flavour).


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