Preheat oven to 400°F. Spray a 10-inch oven-safe skillet with cooking spray. Set aside.

In a large bowl, combine flour, sugar, baking powder, and salt. Add cold butter to the dry ingredients. Using a pastry cutter or your fingers, cut the cubed butter into the flour mixture until the butter pieces are pea-sized or smaller.

In a small bowl, whisk together buttermilk, egg, and vanilla. Pour the wet ingredients into the dry ingredients and stir until just combined. It will have a dough-like consistency.

Transfer to the prepared skillet. Evenly place sliced strawberries on top of the dough.

Bake for 25-30 minutes, or until the shortcake is lightly browned. Allow the cake to cool for about 10-15 minutes before assembly.

While the cake is baking, prepare the strawberry topping. In a large bowl, combine strawberries, sugar, and lemon zest. Place in refrigerator.

Once the cake has cooled slightly, add strawberry topping and whipped cream.

Serve immediately.