Prepare the strawberry filling by combining sliced strawberries, sugar, cornstarch, and lemon juice in a medium saucepan. Cook over medium heat, stirring frequently, until strawberries break down and mixture thickens (about 8-10 minutes). Remove from heat and let cool completely.

Make the vanilla cake by preheating oven to 350°F (175°C). Grease and flour two 8-inch round cake pans. In a large bowl, whisk together flour, sugar, baking powder, and salt. Add softened butter, milk, eggs, and vanilla extract. Beat with electric mixer on medium speed for 2 minutes until smooth and well combined.

Bake the cake layers by dividing batter evenly between prepared pans. Bake for 25-30 minutes, or until toothpick inserted in center comes out clean. Let cakes cool in pans for 10 minutes, then transfer to wire rack to cool completely.

Create the cookie crunch topping by combining crushed cookies, melted butter, and brown sugar in a medium bowl. Mix until crumbs are evenly coated. Spread mixture on baking sheet and bake at 350°F for 5-7 minutes until golden and crispy. Let cool completely.

Whip the cream frosting by beating heavy whipping cream, powdered sugar, and vanilla extract in a chilled bowl until stiff peaks form. Be careful not to overbeat.

Assemble the cake by placing one cake layer on serving plate. Spread half of whipped cream over cake, then top with cooled strawberry filling. Place second cake layer on top. Frost entire cake with remaining whipped cream. Generously sprinkle cookie crunch topping over cake, pressing gently to adhere.

Chill and serve by refrigerating cake for at least 1 hour before serving to allow flavors to meld. Garnish with fresh strawberry slices if desired.