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 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.
Bake for 28-30 minutes or until a toothpick inserted into the center comes out clean.
Remove cakes from the oven and allow to cool in pans for 10 minutes, then turn out onto wire racks to cool completely.
While the cakes are baking, prepare the strawberry filling: In a medium saucepan, combine the chopped strawberries, 1/2 cup granulated sugar, and lemon juice. Cook over medium heat, stirring occasionally, until the strawberries release their juices and the mixture begins to simmer, about 5-7 minutes.
In a small bowl, mix the cornstarch and water until smooth. Stir this slurry into the strawberry mixture.
Continue cooking and stirring until the mixture thickens, about 2-3 minutes. Remove from heat and let cool completely.
Once the cakes and strawberry filling are completely cool, place one cake layer on a serving plate.
Spread the strawberry filling evenly over the top of the first cake layer.
Place the second cake layer on top of the filling.
Optionally, frost the cake with your preferred frosting or dust with powdered sugar before serving.