Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans or line them with parchment paper. In a large mixing bowl, cream together the butter and granulated sugar until light and fluffy (about 3–4 minutes). Add eggs one at a time, beating well after each. Mix in the vanilla extract.

In a separate bowl, whisk together flour, baking powder, baking soda, and salt. Gradually add the dry mixture to the wet ingredients, alternating with the milk. Mix until just combined. Gently fold in the chopped strawberries.

Divide the batter evenly between the two prepared cake pans. Bake in the preheated oven for 25–30 minutes, or until a toothpick inserted into the center comes out clean. Let cakes cool in the pans for 10 minutes, then turn out onto a wire rack to cool completely.

While the cakes are baking, prepare the strawberry filling. In a saucepan over medium heat, combine diced strawberries, sugar, and lemon juice. Cook until strawberries break down and release their juice (about 5–7 minutes). Stir in the cornstarch slurry (cornstarch + water) and cook for another 2–3 minutes until thickened. Remove from heat and cool completely.

In a chilled bowl, beat the heavy whipping cream with powdered sugar and vanilla extract until stiff peaks form. Keep chilled until ready to use.

Place one cake layer on a serving plate. Spread a layer of strawberry filling over the top, leaving a slight border around the edge. Place the second cake layer on top. Frost the top and sides of the cake with whipped cream.

Optionally, pipe extra whipped cream around the edges and top with fresh strawberry slices. Refrigerate for at least 30 minutes before slicing to help the layers set. Serve chilled.