Combine raspberries, granulated sugar, and lemon juice together in a small saucepan over medium heat. Cover and let cook for 3 minutes until the berries are thawed and start breaking down.

Once the raspberries have broken down and are simmering, mix water with cornstarch in a very small bowl. Add the cornstarch mixture and stir it in. Continue to cook and stir until it begins to bubble and thicken.

Remove the pan from heat and pass it through a fine mesh sieve to remove the seeds if desired. Allow the raspberry sauce to cool completely and chill for at least 30 minutes before using.

Preheat the oven to 350°F. Line the base of two 8-inch round cake pans with rounds of parchment paper.

Combine cooled melted butter, oil, sugar and lemon zest in a large bowl and whisk until combined. Whisk in eggs one at a time. Whisk in vanilla and sour cream.

Sift flour, baking powder, baking soda and salt into another bowl. Add the dry ingredients to wet ingredients and fold them in gently.

When they are mostly combined, add milk in 2 stages and fold it in. Use a whisk at the last stage to make a smooth batter, but do not over-mix. Fold in raspberries.

Divide the batter evenly between the prepared pans and bake for 20-25 minutes until lightly golden and a skewer inserted into the center comes out clean. Transfer to a wire rack and let cool completely.

Place cream in a medium bowl and whip until it forms soft peaks. Add the sugar and lemon juice and beat until it forms firm peaks.

Add the raspberry compote and fold it in, keeping chilled until ready to use.

Place soft butter in a large bowl and beat until very smooth and fluffy. Add the powdered sugar and vanilla and slowly beat until it is incorporated.

Gradually beat in the cream until smooth and spreadable, then gradually beat in the compote on low speed.

Place one cake layer on a serving plate. Use a small offset spatula to spread the cream filling over the top, spreading it out to the edges.

Place the other layer on top so it aligns with the sides of the bottom layer. Cover the entire cake with raspberry buttercream.

Use a large offset spatula to even out the sides and make swooshes on the top layer. Decorate with fresh raspberries.