Preheat the oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.
In a medium bowl, whisk together the all-purpose flour, baking powder, and salt. Set aside.
In a large bowl, beat the softened butter and granulated sugar together with an electric mixer on medium speed until light and fluffy, about 3-4 minutes.
Add the eggs one at a time, beating well after each addition. Mix in the vanilla extract.
Alternately add the flour mixture and whole milk to the butter mixture, beginning and ending with the flour mixture. Mix until just combined.
Divide the batter evenly between the prepared cake pans and smooth the tops with a spatula.
Bake for 28-30 minutes or until a toothpick inserted into the center comes out clean.
Remove the cakes from the oven and allow them to cool in the pans for 10 minutes. Then turn them out onto wire racks to cool completely.
While the cakes cool, prepare the raspberry filling. In a small saucepan, combine the fresh raspberries, granulated sugar, and lemon juice. Cook over medium heat, stirring occasionally, until the raspberries release their juices and the mixture begins to simmer, about 5 minutes.
In a small bowl, mix the cornstarch and water until smooth. Stir the cornstarch mixture into the raspberry mixture and cook for another 1-2 minutes until thickened. Remove from heat and let cool completely.
In a medium bowl, whip the heavy whipping cream with powdered sugar and vanilla extract until stiff peaks form.
To assemble the cake, place one cake layer on a serving plate. Spread the raspberry filling evenly over the top.
Spread half of the whipped cream over the raspberry filling.
Place the second cake layer on top and spread the remaining whipped cream over the top and sides of the cake.
Refrigerate the cake for at least 1 hour before serving to allow the filling and whipped cream to set.