Combine blueberries, 3/4 cup sugar, and lemon juice; cook 5 minutes. Transfer berries to a bowl using a slotted spoon. Combine cornstarch and water; add to blueberry liquid, and bring to a boil. Boil 1 minute; stir in blueberries and amaretto. Chill.
Combine 1/4 cup sugar, flour, and next 3 ingredients. Cut in butter with a pastry blender. Combine egg, half-and-half, and extract; reserve 1 tablespoon. Add remaining half-and-half mixture to flour mixture, stirring until dry ingredients are moistened. Turn out onto a floured surface; knead 6 times. Roll to 1/2-inch thickness. Cut 8 shortcakes with a 4 1/4-inch heart-shaped cutter; place on a greased baking sheet. Brush with half-and-half mixture; sprinkle with 1 tablespoon sugar. Bake at 425° for 14 minutes. Let cool.
Beat whipping cream until foamy; add powdered sugar, beating until soft peaks form. Slice each cake in half horizontally. Spoon blueberry sauce over bottom halves; spoon half of whipped cream over berries. Place top half on each. Top with remaining whipped cream; sprinkle with almonds.