• Preheat oven to 400°F. Combine flour, baking powder, sugar, salt, and butter in a food processor and pulse until the mixture resembles coarse sand. Transfer to a bowl, then add 1 egg, 3/4 cup heavy cream, and lemon zest, mixing until a dough forms.
• Form the dough into a disc about 1 inch thick, then cut it diagonally into 6 triangles. Brush the tops with beaten egg and sprinkle with coarse sugar if desired.
• Place the shortcakes on a parchment-lined baking sheet and bake for 15-18 minutes until golden brown. Let them cool for 5 minutes before transferring to a wire rack.
• While shortcakes bake, combine 2 cups blueberries, 1/3 cup sugar, and 1 teaspoon lemon juice in a pot. Boil for 3-4 minutes until berries break down. Thicken with a cornstarch slurry and stir in the remaining 1 cup of blueberries. Set aside to cool.
• Beat 1/2 cup heavy cream until stiff peaks form, then add 2 tablespoons sugar and beat briefly to combine.
• Slice shortcakes horizontally, layer with blueberry sauce, ice cream, and the top half of the shortcake. Finish with a dollop of whipped cream and optional garnishes.

Notes

• Shortcakes and blueberry sauce can be prepared a day in advance. Coarse sugar adds visual appeal. Stirring in fresh blueberries at the end provides a mix of textures. Garnish with mint and lemon slices if desired. Prepare sauce and whipped cream while shortcakes bake for efficiency.