Preheat oven to 350°F. Grease a 9×13 inch baking pan and line with parchment paper if desired.
In a medium bowl, whisk together flour, baking powder, baking soda, and salt. Set aside.
In a large bowl, cream butter and sugar until light and fluffy, about 3 minutes. Add eggs one at a time, beating well after each. Stir in vanilla.
Alternate adding dry ingredients and sour cream-milk mixture, beginning and ending with flour. Mix just until combined.
Pour batter into prepared pan and smooth top. Bake 30-35 minutes until toothpick comes out clean. Cool completely.
Toss sliced strawberries with sugar and let sit 30 minutes to macerate, stirring occasionally.
Beat heavy cream, powdered sugar, vanilla, and pinch of salt until soft peaks form.
Spread whipped cream over cooled cake. Top with strawberries and their juices. Serve immediately or chill 30 minutes for cleaner slices.