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.