Begin by combining granulated sugar and fresh lemon zest in a mixing bowl, blending them together to release the citrus aroma. In another bowl, whisk together all-purpose flour, baking powder, baking soda, and salt. Cut in softened unsalted butter until the mixture resembles coarse crumbs. In a separate container, mix the buttermilk, eggs, and vanilla extract, then gradually combine with the dry ingredients until smooth; this will form the base of your Lemon Raspberry Cake.

Preheat your oven to 350°F (175°C) and grease three 8-inch round cake pans with butter and flour. Divide the lemon cake batter evenly among the prepared pans. Bake for 25-30 minutes or until a toothpick inserted into the center comes out clean. Once baked, allow the cakes to cool in the pans for about 10 minutes before transferring them to wire racks to cool completely, ensuring they develop that perfect, moist texture.

While your cakes cool, prepare the luscious raspberry buttercream. In a mixing bowl, cream together softened unsalted butter and half of the powdered sugar until fluffy. Add in the raspberry purée and incorporate thoroughly, followed by the remaining powdered sugar. Beat the mixture for an additional 2-3 minutes, until it reaches a light and airy texture, perfect for frosting your delightful Lemon Raspberry Cake.

To assemble, place the first lemon cake layer on a serving plate. Spread a thin layer of the raspberry buttercream on top, then pipe a border around the edge and fill the center with raspberry jam, adding rich flavor and texture. Repeat the process with the second layer, then place the third layer on top. Chill the layered cake in the fridge for about 30 minutes to stabilize before frosting the entire outside with remaining buttercream.

Once fully frosted, let your beautiful Lemon Raspberry Cake set in the refrigerator for another 30 minutes to firm up. When ready to serve, slice into portions, allowing the vibrant flavors and moist texture to shine through. For the best taste, let the slices come to room temperature for about 30 minutes before indulging in this scrumptious creation.