Lemon Mousse Cake

This is a recipe that has been in our family for decades. I think a friend of a family member was a catering lecturer in the college where she worked. I converted it into a Keto-friendly cake using the lemon pound cake recipe that I posted on the blog last year (see below, I’ve included it here). I made a different lemon curd recipe. This is a celebratory cake made as a birthday cake – it’s delicious and feels decadent! It looks more complex than it was to make.

To give the overall approximate net carbs, I calculated the whole lemon mousse topping as lemon curd (8 Tbspns) 4g carbs, double cream 6g carbs and the cream cheese 6g carbs with a total of 16g carbs. The cake is cut into 16 slices, the topping provides 1g carb/slice. The lemon pound cake is 3.9 net carbs. I calculated that a 1/16th slice of this lemon mousse cake is 4.9g carbs. Be careful as you slice it as it’s so good there’s a tendency to encroach on the next slice.

Lemon Pound Cake

Nutrition lemon pound cake (1 slice): 174 cals | 5.1g carbs | 1.2g fibre | 10.9g fat | 1.1g sugar | 3.9g net carbs.

Lemon pound cake | Prep time: 15 mins | Cook time: 50 mins | Servings: 16

Ingredients for Lemon pound cake:

  • 5 eggs – at room temperature
  • 3/4 cup/150g erythritol or xylitol
  • 1/2 cup/120ml melted coconut oil or melted butter (I used lactose free butter)
  • 2 cups/220g almond flour 
  • 1/4 cup/35g coconut flour 
  • 1 tablespoon baking powder
  • 1/4 cup/60ml lemon juice 
  • 1/2 tablespoon lemon zest – optional (you definitely need the lemon zest)

Method for the Lemon Pound Cake

  • Preheat oven to 350F/180C/160C fan-assisted. 
  • Line an 8 inch round cake tin with a piece of parchment paper.
  • Slightly oil the paper to make sure the pound cake doesn’t stick. Set aside. 
  • In a medium mixing bowl, whisk together the eggs, erythritol, melted butter and lemon juice. Make sure that your butter is not too hot or it will ‘cook’ the eggs and create lumps. 
  • NOTE: All your ingredients must be roughly at same temperature, think room temperature, especially the eggs and lemon juice. Cold ingredients, just out of the fridge will solidify the coconut oil creating oil lumps, or use melted butter to prevent this happening. Then, set aside. 
  • In a different large mixing bowl, whisk together the almond flour, coconut flour and baking powder. Stir to evenly combine, then add the lemon zest.
  • Pour the liquid ingredients into the dry ingredients.
  • Stir all the ingredients together with a spatula until it forms a consistent cake batter with no lumps. Combine for at least 2 minutes to make sure the coconut flour fibre absorbs the moisture. 
  • Transfer the cake batter into your chosen tin. Make sure you are aware of the cooking times for the loaf cake and if you decide to use an alternative tin that you monitor the cake carefully after about 45-50 minutes.
  • Place the baking tin in the centre of your oven and bake at 180C /160C fan-assisted (350F). After 15 minutes decrease temperature to 160C/140C (320F) and cover the cake with a loose piece of foil. This will prevent the top of the cake from burning and enable the middle to bake slowly. Keep baking for 45- 60 minutes in total, or until a toothpick inserted in the centre of the cake comes out with little to no crumbs on it. Note: the 8 inch cake cooked in 50 minutes total because it was thinner.
  • Cool for 10 minutes in the tin, then turn the cake out.
  • Transfer to a cooling rack to cool completely. It takes approximately 3 hours to cool fully. 

Lemon curd (Yield 1 1/2 cups) | Prep time: 15 mins | Cook time: 10 mins | Servings: 10

Nutrition lemon curd (2 tbsp): 98 cals | 1g net carbs | 10g fat | 1g Protein

Ingredients for sugar-free lemon curd:

  • 1/2 cup butter (I used lactose free)
  • 1/2 cup fresh lemon juice
  • 1/2 cup/65g xylitol (or other equivalent zero calorie sweetener)
  • 1/4 cup lemon zest
  • 6 large egg yolks 

Method for the lemon curd:

  • Melt the butter in a small saucepan on low heat
  • Remove pan from the heat and whisk in the sweetener, lemon juice and lemon zest until dissolved.
  • Whisk in the egg yolks and return the pan to the stove over a low heat.
  • Whisk continually until the curd starts to thicken.The lemon curd, will thicken suddenly. 
  • Note: I kept removing the pan from the heat and stirring to ensure it didn’t over cook and remained smooth.
  • Remove the pan from the heat and strain the curd into a small bowl to remove the zest.
  • Let cool to room temperature, then cover and store in the fridge for up to one month.

Constructing the Lemon Mousse Cake

Making the Lemon Mousse Filling

Ingredients

  • 5 ounces cream cheese (I used lactose-free)
  • Cup of double cream (I used plant-based double cream)
  • 1/2 cup of lemon curd (see recipe above)
  • 1 (12g) sachet of gelatine granules
  • 1/4 cup of fresh lemon juice (optional)

Note: taste the mixture when prepared for balance of sweet and sourness. If necessary whisk in a little more finely ground erythritol if needed. Be careful as you need the contrast between the cake and the filling.

Method

  • Sprinkle the gelatine into a little hot water in a small bowl (approx. 8tbsp). Stir briskly until thoroughly mixed. You may need to put the bowl into a pan of hot water to help the gelatine to dissolve fully.
  • Note 1: 12g gelatine will set approximately 1 pint of ‘liquid’.
  • Note 2: Always add the gelatine to the hot liquid and not the other way round.
  • Whisk together the cream cheese and double cream until thickened.
  • Then, whisk in the lemon juice and lemon curd.
  • Continue to whisk and slowly add the gelatine a little at a time until it’s mixed in. I always drizzle the gelatine into a mixture at the side of the bowl.

Putting the cake together

  • Slice the cake horizontally when cool.
  • Place the bottom part of the split cake back into the baking tin lined with tinfoil or greaseproof paper with an over hang so you can lift the mousse cake out of the tin. Ideally this should be a loose bottomed baking tin but mine broke and I haven’t replaced it.
  • Pour the mousse filling over the bottom of the cake and smooth it out. Then, put in the fridge for a few hours to set.
  • Split the cake top into 16 pieces ready for completing the cake.
  • When the filling is set, remove from the fridge and place the 16 pieces of cake on to the mousse filling. Dredge with keto icing sugar. Store in the fridge until required.
  • This cake kept well for 4-5 days, covered in the fridge. It really is a wonderfully luscious cake for a celebration.
  • Enjoy!

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