Preheat oven to 425°F (220°C). Line a baking sheet with parchment paper.
In a medium bowl, combine sliced strawberries, granulated sugar, and lemon juice (if using). Toss well and let sit for at least 30 minutes, stirring occasionally, to create a juicy syrup.
In a large bowl, whisk together flour, baking powder, baking soda, salt, and sugar. Cut in the cold butter using a pastry cutter until the mixture resembles coarse crumbs. Add the cold buttermilk and stir just until combined—do not overmix.
Turn dough out onto a lightly floured surface and gently pat it into a 1-inch thick rectangle. Use a biscuit cutter or glass to cut out 6 rounds. Place them on the prepared baking sheet and brush tops with a bit of buttermilk.
Bake for 12–15 minutes or until golden brown. Remove from oven and cool slightly on a wire rack.
In a separate bowl, beat heavy cream, powdered sugar, and vanilla extract until soft peaks form.
To assemble, split each biscuit in half horizontally. Place the bottom half in a bowl, spoon a generous amount of strawberry mixture over it, add the top half of the biscuit, and top with whipped cream and more strawberries if desired.