Make the Raspberry Filling:

In a small saucepan, combine raspberries, sugar, and lemon juice. Cook over medium heat until raspberries release their juices.

Stir cornstarch and water in a small bowl, then add to the pan.

Bring to a simmer and stir until thickened (about 5–7 minutes).

Strain through a sieve if a seedless filling is desired. Let cool completely before using.

Prepare the Cake Layers:

Preheat oven to 350°F (175°C). Grease and line three 8-inch cake pans with parchment paper.

In a medium bowl, whisk together flour, baking powder, and salt.

In a large mixing bowl, cream butter and sugar on medium-high speed until light and fluffy, about 3–4 minutes.

Add eggs one at a time, mixing well after each. Mix in vanilla.

Combine milk and sour cream.

Add the dry ingredients in three parts, alternating with the milk mixture, beginning and ending with the dry. Mix until just combined.

Divide the batter evenly between pans.

Bake for 25–30 minutes, or until a toothpick inserted comes out clean. Cool in pans for 10 minutes, then transfer to wire racks to cool completely.

Make the White Chocolate Buttercream:

Beat butter on medium-high until fluffy (about 2 minutes).

Add melted white chocolate and beat until smooth.

Gradually add powdered sugar, then vanilla, salt, and cream. Beat until light and fluffy, adding more cream if needed.

Assemble the Cake:

Level cake layers if necessary.

Place the first layer on a cake board or plate. Pipe a buttercream border around the edge and fill the center with raspberry filling.

Repeat with the second layer.

Top with the third layer and frost the entire cake with white chocolate buttercream.

Optional: Decorate with fresh raspberries and white chocolate shavings.