1. Prepare Shortcakes: Preheat oven to 425°. Stir together first 5 ingredients in a large bowl. Cut butter into flour mixture with a pastry blender or fork until mixture resembles coarse meal. Make a well in center of mixture.
2. Stir together 1 cup cream and 1/2 tsp. lemon extract. Add to dry ingredients, stirring just until dough comes together.
3. Turn dough out onto a lightly floured surface; knead lightly 2 to 3 times. Pat or roll dough to 1-inch thickness; cut into 8 rounds with a 2 1/4-inch round cutter. Place 2 inches apart on a parchment paper-lined baking sheet.
4. Stir together egg yolk and remaining 3 Tbsp. cream; brush over tops of shortcakes. Sprinkle with sparkling sugar.
5. Bake at 425° for 15 minutes or until golden. Cool completely (about 30 minutes).
6. Prepare Topping: Beat 1 1/2 cups heavy cream and 1/4 tsp. lemon extract at medium speed with an electric mixer until foamy. Gradually add powdered sugar, beating until soft peaks form.
7. Toss together oranges, grapefruit, mint, and 1/4 cup granulated sugar. Split shortcakes in half lengthwise. Top bottom halves of shortcakes with half of fruit and whipped cream. Cover with top halves of shortcakes, and top with remaining fruit mixture and whipped cream.