Macreate the berries: In a large bowl, combine the berries, sugar, lemon zest, and lemon juice. Toss gently. Let sit at room temperature for 20–30 minutes to release juices. Chill until ready to use.

Preheat the oven: Set your oven to 425°F (220°C). Line a baking sheet with parchment paper.

Mix the dry ingredients: In a large bowl, whisk together flour, granulated sugar, baking powder, baking soda, and salt.

Cut in the butter: Add the cold butter cubes. Using a pastry cutter or your fingertips, work the butter into the flour until the mixture looks like coarse crumbs with pea-sized bits. Keep it cold.

Add liquids: Stir together buttermilk and vanilla. Pour into the flour-butter mixture. Gently mix with a fork until the dough just comes together. If dry, add 1–2 teaspoons more buttermilk.

Shape the dough: Turn out onto a lightly floured surface. Pat into a 1-inch thick round. Fold it over onto itself once or twice to create layers, then pat back to 1-inch thickness.

Cut the shortcakes: Use a 2 1/2–3-inch round cutter, pressing straight down (don’t twist) to cut 6–8 rounds. Place on the prepared baking sheet, spacing them an inch apart. Re-form scraps gently as needed.

Top and bake: For a golden finish, whisk the egg with 1 tablespoon water and brush the tops lightly. Sprinkle with coarse sugar if you like. Bake 12–15 minutes, until risen and golden brown. Cool on a rack for at least 10 minutes.

Make the whipped cream: In a chilled bowl, beat the cold heavy cream, powdered sugar, vanilla, and a pinch of salt to soft peaks. Don’t overwhip; it should be smooth and billowy.

Assemble: Split warm or room-temperature shortcakes with a serrated knife. Spoon berries and their juices over the bottom halves. Add a generous dollop of whipped cream, then cap with the top halves. Finish with more cream and a few extra berries if you like.