Preheat your oven to 400°F (200°C). Line a 9x13 inch baking pan with parchment paper, leaving overhang on the sides for easy removal.
In a large bowl, whisk together the flour, granulated sugar, baking powder, and salt until evenly combined, then create a well in the center.
Add the cold cubed butter to the flour mixture and use a pastry cutter or two forks to cut it in until the mixture resembles coarse crumbs with pea-sized butter pieces — work quickly to keep everything cold.
In a medium bowl, whisk together the heavy cream, egg, and vanilla extract until fully combined, then pour into the well in the dry ingredients.
Gently stir until just combined — the dough will be slightly sticky and shaggy with a few dry streaks, which is perfect; do not overmix.
Transfer the dough to the prepared pan and use lightly floured hands or a spatula to press it evenly to about 1 inch thick, reaching all corners.
Brush the top generously with melted butter and sprinkle with coarse sugar, then bake for 22–25 minutes until golden brown and a toothpick inserted in the center comes out clean.
Let the shortcake cool in the pan for 10 minutes, then use the parchment overhang to transfer it to a wire rack to cool completely before topping.
Combine the berries with sugar, lemon juice, and lemon zest in a bowl; toss gently and let sit for 15–20 minutes until the berries release their juices.
Beat the cold heavy cream, powdered sugar, and vanilla extract on medium-high speed until soft peaks form — stop before it becomes grainy or butter-like.
Cut the cooled shortcake into 12 squares, then top with the macerated berries and their juices and generous dollops of whipped cream; serve immediately.