Gently toss sliced strawberries with sugar, cornstarch, lemon juice, and zest in a large bowl. Allow to macerate for at least 15 minutes while preparing the biscuit dough.
Place a 10-inch cast iron skillet in the oven and preheat to 425°F (220°C).
In a large bowl, whisk together flour, sugar, baking powder, and salt. Using a pastry cutter or two forks, cut in the cold butter until the mixture resembles coarse crumbs with some pea-sized pieces remaining.
In a separate small bowl, whisk together the buttermilk, egg, and vanilla extract. Pour this mixture over the flour mixture and stir just until combined (avoid overmixing).
Carefully remove the hot skillet from the oven using oven mitts. Add a tablespoon of butter and swirl to coat the bottom and sides. Pour the strawberry mixture into the hot skillet, then drop spoonfuls of the biscuit dough evenly over the top, leaving some gaps for the strawberry juices to bubble through. Sprinkle with turbinado sugar.
Bake for 22-25 minutes, or until the biscuit top is golden brown and a toothpick inserted into the center comes out clean. The internal temperature should reach 200°F for perfect doneness.
Allow to cool for 15 minutes before serving. Top with freshly whipped cream and optional mint leaves or honey drizzle.