To make the compote, combine strawberries, sugar, lemon zest, lemon juice and cornstarch to a saucepan and cook over medium heat. Stir constantly until a sauce forms. Set aside to cool
Preheat oven to 400°F. Coat your pan (preferably a 10-inch cast iron skillet) with butter and flour, shaking out any excess flour
In a bowl, whisk together flour, baking powder, sugar and salt until combined
In a larger bowl, mix together egg, vanilla, whole milk and buttermilk. Stir in melted butter and dry ingredients then mix until just incorporated
Pour about half of the cake batter into the pan and then layer with about three-quarters of the strawberry compote Add remaining cake batter and then dollops of remaining compote. swirl together with a butter knife
Bake until golden brown and an inserted toothpick comes out clean, about 25 minutes
Serve warm with whipped cream