Preheat your oven to 350°F (175°C). Grease and line the bottom of the cake pans with parchment paper.
In a large mixing bowl, cream together the softened butter and granulated sugar until light and fluffy, about 3-4 minutes.
Add the eggs one at a time, mixing well after each addition, then mix in the vanilla extract.
In another bowl, whisk together the flour, baking powder, and salt.
Gradually add the dry ingredients to the butter mixture, alternating with the milk. Mix until just combined.
Divide the batter evenly between the prepared cake pans. Smooth the tops with a spatula.
Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted in the center comes out clean.
Allow the cakes to cool in the pans for 10 minutes before transferring them to a cooling rack to cool completely.
While the cakes are cooling, prepare the raspberry filling by combining the raspberries, sugar, cornstarch, and lemon juice in a saucepan. Cook over medium heat until the mixture thickens and starts to bubble, about 5-7 minutes. Remove from heat and let cool.
For the buttercream frosting, beat the softened butter in a mixing bowl until creamy. Gradually add the powdered sugar, mixing until smooth. Add the vanilla and heavy cream, mixing until fluffy and spreadable.
Once the cakes have completely cooled, level the tops if necessary. Place one layer on a cake stand, spread a layer of raspberry filling, and then a layer of buttercream frosting.
Place the second cake layer on top and frost the top and sides of the cake with the remaining buttercream.
Decorate as desired with fresh raspberries, edible flowers, or additional frosting.
Slice and serve your beautiful J'Adore Layer Cake!