Prepare the blueberries: In a saucepan over medium heat, combine blueberries, 1/4 cup sugar, and lemon juice. Cook until berries break down and release juices. If thicker sauce is desired, stir in cornstarch mixed with water and cook until thickened. Let cool.

1. Make the shortcakes: In a large bowl, whisk together flour, baking powder, salt, and 1/4 cup sugar. Cut in cold butter until mixture resembles coarse crumbs.
2. Add wet ingredients: Stir in heavy cream and vanilla until just combined. Do not overmix.
3. Shape and bake: Turn dough onto a floured surface, gently knead, and pat into 1-inch thickness. Cut into rounds with a biscuit cutter. Place on parchment-lined baking sheet and bake at 400°F (200°C) for 15–18 minutes, until golden brown. Cool on wire rack.
4. Assemble: Slice shortcakes in half horizontally. Spoon blueberry mixture over bottom halves, top with whipped cream, then place the other halves on top. Serve immediately.