Preheat the oven to 350°F (175°C). Grease two 8-inch (20 cm) round cake pans, line bottoms with parchment, and lightly flour the sides. Set out all ingredients to come to room temperature before you start mixing.

In a medium saucepan, combine raspberries, 60g sugar, and 2 tsp lemon juice. Cook over medium heat, stirring and mashing berries until the mixture thickens, about 10-12 minutes. Press through a mesh sieve to remove seeds. Cool to room temperature before using.

In a medium bowl, whisk together flour, baking powder, baking soda and salt until fully combined. Set aside, uniformly blended dry ingredients ensure even leavening and a consistent crumb in your layers.

In a stand mixer with paddle attachment, beat 200g butter, 340g sugar, and lemon zest on medium speed for 3-4 minutes, until very pale and fluffy. Scrape bowl, well-creamed butter and sugar aerate the batter for a tender, light cake.

Add eggs one at a time to the creamed butter mixture, mixing fully between each addition. Beat in vanilla and 80ml lemon juice just until incorporated. The batter may look slightly curdled after adding the juice; this is normal and will smooth out after adding dry ingredients.

Reduce mixer to low. Add half of the flour mixture, blend just until combined. Add all of the sour cream and the milk, mixing gently. Finish with remaining flour blend, mixing just until you see no dry streaks. Do not overmix; stop as soon as batter looks smooth.

Divide cake batter evenly between the two prepared pans. Dollop spoonfuls of cooled raspberry jam over each, using about one-third of the jam total and swirling gently into the surface with a skewer or butter knife. Reserve remaining jam for assembly.

Bake both pans for 28-32 minutes, rotating pans halfway, until cakes are golden and the centers spring back when lightly pressed. A toothpick inserted near the center should come out clean or with a few moist crumbs. Cool in pans on racks for 10 minutes, then turn out and peel away parchment.

Let cakes cool fully on wire racks (about 1 hour). If domed, use a long serrated knife to level tops for even stacking, this helps the layers stay stable and look professional once filled and frosted.

In a clean stand mixer, beat 225g softened butter on medium for 2 minutes. Gradually add powdered sugar, mixing on low. Beat in vanilla and 1-2 tbsp milk, then add salt if using. Whip on medium-high until fluffy and pale, about 2 minutes more, scraping bowl once for consistency.

Set the first cake layer on a serving plate. Pipe or spread a thin ring of buttercream to create a border, then spread half of the remaining raspberry jam inside the ring. Top with a thin, even layer of frosting, then place second cake layer on top.

Spread a super-thin layer of buttercream over top and sides to trap crumbs. Chill cake for 20 minutes to set. For the semi-naked look, add more frosting sparingly and use an offset spatula to sweep off almost all excess, letting cake and fruit show through the buttercream.