Instructions

Cake

1. Prep: Preheat oven to 350°C/175°C. Grease and line the bottoms of three 8 inch round cake pans. Set aside.
2. Dry Ingredients: Whisk and sift the flour, xanthan gum, baking powder and salt in a large bowl. Set aside.
3. Heat Milk: In a small sauce pot, warm the butter and milk over a medium heat. Warm until the milk is just about to boil and the butter has melted. Add the vanilla extract and lemon juice. Set aside for now.
4. Eggs + Sugar: Add the eggs and sugar to another large mixing bowl or to the bowl of a stand mixer. Beat on a high speed i the stand mixer or with a handheld mixer, about 3-5 minutes until the mixture is pale-yellow, thick, glossy and has tripled in volume.
5. Fold Flour: In three stages, add the flour mixture to the egg mixture. Use a wooden spoon or rubber spatula to fold the flour into the eggs. Work slowly and carefully to avoid over mixing the batter. Continue until all the flour has been added and fully mixed in to the batter. The batter should be thick and airy.
6. Add Remaining Wet Ingredients: Add the warmed milk mixture and lemon zest. Mix gently with a large whisk until smooth and just combined.
7. Divide: Pour the batter into the prepared pans. Each pan should hold about 200g of batter. Gently lift up the tins and drop them on a counter/table surface to get rid of air bubbles.
8. Bake: Place in the middle of the oven and bake for about 18-20 minutes. To check for doneness, insert a knife or tooth pick into the center of the cake. If it comes out clean with only a few moist crumbs, it's done.
9. Cool: Let cool in the tin for about 5 minutes then flip over onto a cooling rack. Cool completely before frosting.

Filling

1. Add berries, sugar, lemon juice and vanilla to a small sauce pot. Mix together and bring to a boil, then reduce the temperature to main a simmer.
2. Let simmer 5-10 minutes, stirring every so often until the berries have broken down. Carefully taste and add more sweetener as you see fit.
3. In a small bowl, whisk together 1 tbsp cornstarch and water. Stir into the pot and cook another minute or so until the berry mixture thickens. Remove from the heat and set aside. Cool completely before adding to the cake.

Frosting

1. Add mascarpone and sugar to a stand mixer bowl or a large mixing bowl. Beat in the mixer or with a hand mixer on high 1-2 minutes until thick and creamy. The sugar crystals should be dissolved or almost fully dissolved.
2. Add the vanilla extract and heavy cream. Beat again, another 1-3 minutes on a medium speed until thick and creamy. The frosting should look smooth and airy. Try not to mix too long or the frosting might start to split (look curdled).

Assemble

1. Place one cake layer on a cake stand or serving plate. Spread a thin layer of frosting over the top. Pipe a border around the outside of the cake to hold the filling in.
2. Add about 1/3 cup filling in the middle of the cake border. Try not to add so much filling that it flows over the top of the frosting border or it will spill out the sides. Repeat with the remaining cake layers.
3. Optional: Make a crumb coating. Spread a thin layer of frosting all over the sides and top of the cake, then chill for 10-15 minutes before frosting the rest. This will make for a smoother frosting layer with less crumbs mixed throughout.
4. Add a few spoonfuls of the remaining berry filling to the frosting bowl and mix together. Mix fully or leave it partially unmixed to maintain a rippled, berry look. Frost the outside of the cake with the remaining frosting and decorate as desired and enjoy.