Let’s assemble this beautiful Berry Cake with its delicate Lemon Mousse! First, ensure your three 8-inch yellow cake layers are baked and completely cooled. If they have significant domes, you may want to level them with a serrated knife for easier stacking, though it’s less critical for a naked cake.

Now, make the Lemon Mousse. Separate 3 of the large eggs, placing the yolks in a large heatproof bowl and the whites in a separate, clean, grease-free mixing bowl (set whites aside for later). Add the 3 remaining whole eggs to the bowl with the yolks. Whisk in 1 cup of the granulated sugar, the fresh lemon zest, the fresh lemon juice, and a pinch of salt.

Create a double boiler: Fill a large saucepan with a few inches of water and bring it to a gentle simmer over medium heat. Place the heatproof bowl containing the egg yolk mixture over the simmering water, ensuring the bottom of the bowl does not touch the water. Cook the mixture, stirring constantly and scraping the bottom and sides with a wooden spoon or heatproof spatula, for about 15 minutes. The mixture will thicken slightly, enough to coat the back of the spoon (like a thin custard or crème anglaise). Do not let it boil or the eggs will scramble.

Remove the bowl from the heat and set it aside for about 15 minutes to cool slightly. Pour the thickened lemon mixture into a clean bowl. Press a piece of plastic wrap directly onto the surface of the mixture (this prevents a skin from forming). Refrigerate this lemon base for at least 1-2 hours, or until completely chilled through.

Once the lemon base is thoroughly chilled, prepare the meringue component. Add the 3 reserved egg whites to their clean, grease-free mixing bowl. Using an electric mixer (stand or hand) with clean whisk attachments, beat the egg whites on high speed for about 1 minute until frothy and opaque. Gradually add the remaining 2 tablespoons of granulated sugar while beating. Continue to beat on high speed until the whites form stiff, glossy peaks (they should hold their shape completely when the whisk is lifted).

Prepare the whipped cream component. In a separate (preferably chilled) bowl, pour the 1 cup of cold heavy whipping cream. Using clean whisk attachments, beat on high speed until stiff peaks form. Be careful not to overwhip into grainy butter.

Now, assemble the mousse – this requires gentle folding! Retrieve the chilled lemon base from the refrigerator. Gently fold the stiffly beaten egg whites (meringue) into the cold lemon mixture using a large rubber spatula. Add about one-third of the whites first to lighten the lemon base, then gently fold in the rest until just combined, trying not to deflate the whites too much.

Next, gently fold the stiffly whipped cream into the lemon-meringue mixture. Again, add about one-third first to lighten, then fold in the remainder gently but thoroughly, scraping from the bottom, until the mousse is uniform in color and texture. Avoid overmixing. Chill the finished mousse for at least 30 minutes before assembling the cake to allow it to firm up slightly.

Prepare the berries for assembly. Gently rinse all fresh berries and pat them completely dry with paper towels. Slice the strawberries.

Assemble the Berry Cake. Place one cooled cake layer onto your serving plate or cake stand. Optional: drizzle the layer lightly with honey. Spoon about ½ to ⅔ cup of the chilled lemon mousse onto the center of the cake layer. Using an offset spatula, gently spread the mousse towards the edges, but leave about a 1-inch border of plain cake around the circumference (this helps prevent mousse from squeezing out excessively in the naked style).

Arrange a generous, single layer of mixed fresh berries (including sliced strawberries) over the mousse layer, staying within the mousse boundary. Carefully place the second cake layer on top. Repeat the process: drizzle with honey (optional), spread with mousse (leaving a border), top with an assortment of berries. Place the third and final cake layer on top. You can add a final thin layer of mousse and arrange berries decoratively on the very top, or leave the top cake layer plain.

For the naked cake finish, you can either leave the sides completely bare, showing the layers of cake, mousse, and berries, or use an offset spatula to scrape down any mousse that squeezed out, creating a very thin, translucent veil of mousse on the sides.

Refrigerate the assembled cake for at least 30 minutes (longer is better, up to a few hours) before serving. This allows the mousse to set fully and makes slicing easier. If desired, garnish with edible chamomile flowers or other edible flowers just before serving.