Mix sliced strawberries with granulated sugar and let them sit to thicken. This can be done ahead of time, even a few hours before serving.

In a large mixing bowl, combine the flour, granulated sugar, kosher salt, and baking powder. Whisk well.

Chop the cold butter into small pieces and add it to the flour mixture. Use a pastry cutter to mix until it resembles coarse crumbs the size of peas.

In a separate measuring cup, whisk the large egg into the cold buttermilk and stir this into the flour mixture, creating a shaggy dough. If it feels too dry, add a little cold buttermilk or ice water.

Move the dough to a floured surface and gently knead it just until it comes together. Roll it out into a rectangle about 9x13 inches thick.

Fold the dough into thirds, pat it down gently, and roll it out again to about 1¼ inches thick.

Use a floured 2½-inch biscuit cutter to cut out the shortcakes, re-rolling scraps as necessary. Place them in a buttered cast iron skillet or greased baking dish, making sure they touch slightly.

For the best texture, freeze the dough for 20 minutes while preheating your oven to 425°F (220°C).

Just before baking, brush the tops with buttermilk or cream and sprinkle with sugar. Bake for 18-22 minutes until golden brown.

In a bowl, beat the heavy cream with powdered sugar and vanilla until stiff peaks form.

Serve warm shortcakes by slicing them in half and layering with strawberry topping and whipped cream. Top with the other half and add more strawberries and cream.