Luscious lemon mousse cake might be the perfect layer cake. Lemon cake with Limoncello syrup, zesty lemon curd and creamy lemon mousse. (Limoncello liquor is optional.)
I am so excited to share this recipe with you! For many years this was the most popular cake flavor for my custom cake business. Once I introduced the Chocolate Chip Cookie Cake the two cake flavors shared top billing. For the last 5 years I’d say almost half the wedding cakes I sold had two different flavors in the cake; half the servings with the cookie flavor, and the other half with Luscious Lemon Mousse Cake. And this cake is truly luscious!
Yes, this cake is a little bit of a project. But I think it’s totally worth the effort, especially for a special occasion. If you watch the video you’ll see the entire process. It is sped up, but you can see how easily the whole thing comes together once you have all the components in place.
“Liason” the gelatin for a perfectly smooth Lemon Mousse cake filling:
The step that might be the most unfamiliar to non-pastry-chefs is how to “liason” or “temper” the gelatin into the mousse. Tempering gelatin is similar to the process for tempering eggs into hot milk to make custard.
If you simply poured the warm gelatin into the cool mousse it might immediately set into little rubbery lumps. Definitely not the texture we’re going for here. By whisking a scoop of mousse into the melted gelatin we bring the two ingredients closer together in texture and temperature. Now we have silky-smooth mousse. The filling is set with just enough gelatin to hold it together when the cake is sliced.
The limoncello makes the flavor extra special. Of course, if you can’t or don’t want to do liquor you can leave it out. You can use water to bloom the gelatin. But even if you generally aren’t a fan of liquor flavors I suggest you give it a try. The limoncello adds a deep lemon flavor without leaving a boozy aftertaste. You can check out this post to see why alcohol enhances flavor.
Watch the recipe video to see how-to make a Luscious Lemon Mousse Cake from start to finish.
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- 1 recipe Vanilla Butter Cake
- Grated zest from 1 lemon
- 2 teaspoons lemon extract
- 1 Recipe Lemon Curd divided. Use 1 1/4 cups (12 oz, 340g) for the mousse
- 1 cup (8 oz, 236ml) heavy cream
- 2 tablespoons powdered sugar
- 1 1/2 teaspoons gelatin powder
- 3 tablespoons (1.5 oz, 44ml) Limoncello (use water if you want to avoid alcohol)
- 1 teaspoon lemon extract
- Mix the cake according to the recipe, adding the zest to the dry ingredients and the lemon extract with the vanilla.
- Divide the batter between two 8" pans lined with a parchment round or buttered and floured. Bake as instructed in the recipe. Wrap the cooled layers and chill until firm (I like to bake the cake a day ahead)
- When you're ready to assemble the cake, trim the browned edges and domed top off both cakes. Split each cake horizontally so you have a total of 4 cake layers. See how to prep the layers here . Have your syrup and buttercream ready before you begin making the Lemon Mousse.
- Place the Limoncello (or cold water) and lemon extract into a microwave safe bowl. Sprinkle the gelatin over the liquid, whisk briefly to combine and set aside to bloom. Whip the cream with the powdered sugar and set aside.
- Place 1 1/4 cups of the lemon curd in a large mixing bowl and use a spatula to smooth out the curd to break up any lumps. (Save the rest for filling and finishing the cake). Fold 1/3 of the the cream into the lemon curd until no lumps of curd remain. Fold in the remaining cream until it's about 1/2 way incorporated.
- Heat the bloomed gelatin in the microwave in 10 second increments until it's hot to the touch. Working quickly, add a 1/2 cup of the mousse to the warmed gelatin. Whisk immediately until completely incorporated. Pour the gelatin mixture back into the mousse. Immediately whisk until the mousse is smooth and the gelatin is evenly incorporated. If the mousse is very soft, refrigerate briefly to let it thicken before assembling the cake.
- Fill a piping bag fitted with a star tip with buttercream (or use a disposable bag with the tip cut).
- Set one layer of the cake, flat side down, onto a cardboard cake round or a serving plate. Brush the layer generously with the Limoncello syrup. Pipe a ring of buttercream around the edge of the layer to form a "dam" for the mousse. Scoop half the lemon mousse onto the layer and smooth until even.
- Gently place the second cake layer onto the mousse, careful not to squish the mousse layer. Sprinkle the layer with syrup and pipe a dam of buttercream. Set aside a 1/2 cup of the lemon curd and scoop the rest onto the layer. Smooth the curd until even (be careful not too press hard or you might squish the mousse layer beneath).
- Place the 3rd cake layer, brush with syrup and pipe a dam. Fill with the remaining lemon mousse. Top with the 4th layer, brush with syrup. Set the cake into the refrigerator for about 20 minutes to set the buttercream "dams" and the mousse.
- Ice the cake with a thin crumb coat of buttercream. Refrigerate the cake for at least an hour to set the buttercream and allow the mousse time to gel. Ice the cake with a final coating of buttercream.
- Use a piping bag fitted with a star tip to pipe a border around the top of the cake. Spread the last 1/2 cup of curd onto the cake. Refrigerate for at least 3-4 hours to make sure the filling is completely set, preferably over night.
- Remove the cake from the refrigerator 1/2 hour before serving.
The cake must be stored in the refrigerator because of the mousse filling. Take the cake out 1/2 hour to an hour before serving to allow it to soften before serving. Leftovers can be refrigerated and the cake freezes very well.
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