In a saucepan, combine sliced strawberries, sugar, and lemon juice. Cook over medium heat until berries soften.

Create a slurry with the cornstarch and a little water, then stir it into the filling. Cook for 1-2 minutes more until slightly thickened. Set aside to cool completely.

Preheat oven to 350°F (175°C). Grease and flour two 8-inch round cake pans.

In a large bowl, cream together softened butter and sugar until light and fluffy. Beat in eggs one at a time, then stir in vanilla.

In a separate bowl, whisk flour, baking powder, baking soda, and salt. Alternately add the dry mixture and buttermilk to the wet ingredients, beginning and ending with the dry. Mix until just combined.

Pour batter evenly into the prepared pans. Bake for 25-30 minutes, or until a toothpick inserted into the center comes out clean. Let cool completely.

In a chilled bowl, beat cold heavy cream to soft peaks. In another bowl, beat softened cream cheese, powdered sugar, and vanilla until smooth. Gently fold the cream cheese mixture into the whipped cream.

Place one cake layer on a serving plate. Pipe a dam of frosting around the edge. Fill with half of the cooled strawberry filling.

Top with the second cake layer. Frost the top and sides of the cake with the remaining frosting. Garnish with fresh strawberries before serving.