Preheat oven to 350°F (175°C). Grease and flour three 6-inch round cake pans. Line the bottoms with parchment paper.

In a medium bowl, whisk together the flour, baking powder, and salt. Set aside.

In a large bowl with an electric mixer, cream the softened butter and granulated sugar on medium-high speed until light and fluffy, about 3-4 minutes.

Add the eggs one at a time, beating well after each addition. Scrape down the sides of the bowl as needed. Beat in the lemon zest and vanilla extract.

In a separate small bowl, combine the lemon juice and buttermilk.

Gradually add the dry ingredients to the wet ingredients in three additions, alternating with the buttermilk mixture, beginning and ending with the dry ingredients. Mix on low speed until just combined after each addition; do not overmix.

Divide the batter evenly among the prepared cake pans.

Bake for 25-30 minutes, or until a wooden skewer inserted into the center comes out clean.

Let the cakes cool in the pans for 10-15 minutes before inverting them onto a wire rack to cool completely. This typically takes at least 45 minutes to an hour.

In a medium saucepan, combine the diced strawberries, granulated sugar, and lemon juice. Cook over medium heat, stirring occasionally, until the strawberries begin to soften and release their juices, about 5-7 minutes.

In a small bowl, whisk together the cornstarch and water until smooth to create a slurry.

Pour the cornstarch slurry into the simmering strawberries and stir continuously. Continue to cook for 1-2 minutes, or until the mixture thickens to a jam-like consistency.

Remove from heat and transfer the strawberry filling to a heatproof bowl. Let it cool completely. It will thicken further as it cools.

In a large bowl with an electric mixer, beat the softened cream cheese and butter on medium-high speed until smooth and creamy, about 2-3 minutes.

Gradually add the sifted powdered sugar, 1 cup at a time, mixing on low speed until incorporated, then increasing to medium speed.

Add the lemon zest, lemon juice, vanilla extract, and pinch of salt. Beat on medium-high speed until the frosting is light, fluffy, and well combined, about 2-3 minutes. If the frosting is too thick, add a tiny bit more lemon juice or milk; if too thin, add more powdered sugar.

Once the cake layers and strawberry filling are completely cooled, level the cake layers if necessary using a serrated knife for a neat presentation.

Place one cake layer on your serving plate or cake stand. Spread about 1/2 cup of the lemon cream cheese frosting evenly over the top.

Pipe a dam of frosting around the edge of the first cake layer (this helps contain the filling). Fill the center with half of the cooled strawberry filling.

Carefully place the second cake layer on top. Repeat the frosting dam and filling process with the remaining strawberry filling.

Place the third cake layer on top. Cover the entire cake with a thin "crumb coat" of frosting and chill in the refrigerator for 15-20 minutes to set.

Once chilled, apply the remaining frosting to the top and sides of the cake, decorating as desired with an offset spatula.

Optionally, garnish with fresh strawberries and extra lemon zest.

Chill the cake for at least 30 minutes before slicing and serving for the best set and clean slices.