When you can’t decide between a Boston Cream Pie or the Chocolate Mousse Cake, you make both!
Boston Mousse Cake will become your new go to recipe for every occasion!
Layers of vanilla cake and chocolate cake with vanilla custard and chocolate mousse filling!
All the elements of the Boston Cream Pie and the Chocolate Mousse cake
Joined together in delicious matrimony with ganche icing draped over the entire cake
I’ve been lightening up my baking since the start of 2023 by using sugar alternatives in many of my bakes
The great news is you can implement those healthier choices in every recipe I am making today!
From both cake recipes to both fillings and even a ganache icing can all be made sugar free!
CLICK HERE FOR MORE ABOUT SUGAR FREE BAKING!
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Notes for Success:
Cornstarch is a very difficult ingredient to measure consistently with a volume/spoons measure
So while I list both measures below I cannot stress enough how the grams measure with a scale is going to give you the best results.
Many times people have complained that their custard is like rubber and they don’t know why!
Agar powder is not necessary in the chocolate mousse as it will set fine without it
However I do like to add it for that extra stability in a cake like this one!
Note that it will set really fast if you are using it though so be sure to work just as fast!
In the video I ended up making a 4 layer cake but my intention was to make a 5 layer cake.
The recipes below are listed for a 5 layer cake for 3-7″ Vanilla Cake Layers and 2- 7″ chocolate layers
So if you only want to make four layers, simply wrap that extra layer and keep it int he freezer for another project!
WATCH THE FULL YOUTUBE VIDEO TUTORIAL FOR HOW TO MAKE THE BOSTON MOUSSE CAKE
Boston Mousse Cake
Ingredients
For the Custard:
- Plant Milk 2¼ cup (533ml)
- Granulated Sugar ¾ cup (150g)
- Cornstarch 5 Tablespoons (40g)
- Turmeric ¼ teaspoon
- Vegan Butter 1½ Tablespoons (21g)
- Vanilla Extract 1 teaspoon (5ml)
For the Chocolate Mousse:
- Semi Sweet Vegan Chocolate 8ounces (226g)
- Hot brewed coffee 2 Tablespoons (30ml)
- Vanilla Extract 1 teaspoon (5ml)
- Aquafaba *Chickpea Water from Canned Chickpeas ¼ cup (60ml)
- Agar powder 1/8 teaspoon *see note above
- Granulated Sugar 4 Tablespoons (50g)
- Cream Of Tartar ¼ teaspoon
- Coconut Milk Full Fat 1- 15ounce can (*refrigerated overnight)
for the icing
Instructions
- First prepare the chocolate cake recipe as per the instructions on that recipe post and then divide the batter into 2-7" cake pans that have been greased & parchment lined.
- Bake in a preheated 350°F oven for approximately 20 minutes or when they are springy to the touch when you gently press the centers
- Cool the cakes in the pans and then flip them out onto a cooling rack to cool the rest of the way.
- Wash & re-grease & re-parchment line the pans, but this time you need 3-7" cake pans
- Prepare the yellow cake recipe as per the instructions on that recipe post & divide the batter evenly between your prepared pans
- Bake in a preheated 350°F oven for approximately 20 minutes or when they are springy to the touch when you gently press the centers
- Cool the cakes in the pans and then flip them out onto a cooling rack to cool the rest of the way.
- Meanwhile prepare the chocolate buttercream according to the instructions on that recipe post
- Next prepare the custard: combine all the ingredients except for the vanilla extract and the vegan butter in a medium sauce pot over and cook over medium to high heat and bring to a boil stirring constantly to avoid scorching the bottom .
- Once it starts to bubble let it boil on low heat for about 10 seconds.
- Remove from the heat and add the vegan butter and vanilla extract and stir until melted and smooth, reserve aside while you prepare the chocolate mousse recipe
- For the chocolate mousse: Melt the chocolate in a large bowl over a double boiler or in a microwave safe bowl
- Combine the hot coffee. sugar and the agar powder in a small sauce pot and bring it to a rolling boil.Keep it warm or the agar will set and you will have to remelt.
- Next open the can of coconut milk that has been refrigerated overnight and carefully scoop out the fat that is on top and whisk it to smooth medium peaks in a small bowl with a hand whisk
- Add the hot brewed coffee with the agar and then the vanilla extract to the melted chocolate all at once while whisking vigorously to incorporate well.
- Cool the chocolate mixture to about 80°F or tepid to the touch before folding in the whipped cream or it will melt back to liquid.
- Add the reserved whipped coconut cream and whisk smooth
- Whip the aquafaba with the cream of tartar to stiff glossy peaks
- Take a small portion of the AF meringue and fold into the chocolate mixture to lighten.
- Fold in the rest of the AF gently
- Set up your first cake layer in a cake ring mold lined with acetate cake strips *see video tutorial
- Then build the cake inside the ring mold with a chocolate buttercream border to hold everything in, with the warm custard and the freshly made chocolate mousse alternating the cake layers as shown in the video tutorial
Notes
Boston Mousse cake must be kept refrigerated but will be fine out at room temperature for up to 4 hours in a cool shady spot.
This cake will stay fresh in the refrigerator for up to 10 days.
I do not like to freeze custard filled cakes as they tend to get watery & separate on the thaw.
Do you have a cookbook? I was looking and can’t seem to find one – ads drive me nuts. I know they’re integral to a blog but it’s so frustrating so I go for books when possible 🙂
Love your recipes. They’re so creative.
Hi Caitlyn thank you! Yes it’s true ads are really annoying unfortunately it is the only way I get paid (although it’s literally in pennies…..)
I recently implemented the “jump to recipe” button for a better user experience.
Yes I have a cookbook~ thank you for asking. CLICK HERE
also sold at Barnes & Noble
oh my gosh I just couldn’t find it- thank you!!! so excited
Hi Gretchen!
I love your cake recipes. I baked your hazelnut cake for my birthday and it was a hit! I am looking forward to preparing this cake tomorrow, but I have a couple questions. Can I prepare the mousse and custard a day in advance? and assemble all elements of this cake chilled?
Thank you so much!!
Olivia :))
Excellent! I’m happy it turned out well for you!
I think I mentioned in the video tutorial for this cake? that I prefer to build everything on one day this way the mousse & the custard set INSIDE the cake giving it much more stability for each slice rather than scoop & spread an already set custard which breaks the cornstarch bond & runs the risk of a loose runny custard~ although it can certainly be done this way! I think I just like the look of a very clean slice (*especially for photo taking for my website!)
The mousse though is much more forgiving and can be done either way since it stays pretty firm