For filling, in a large saucepan, combine the sugar, cornstarch and water until smooth. Bring to a boil over medium heat. Cook and stir until thickened, 1-2 minutes. Add berries and lemon juice. Set aside to cool. , In a large bowl, combine the flour, sugar, baking powder, salt, cinnamon and mace. Cut in butter to form fine crumbs. Stir in the eggs, milk and vanilla until blended. Divide in half. , Spread half of the batter in two greased 8-in. round baking pans. Divide filling and spread evenly over each. Drop remaining batter by small spoonfuls and spread evenly over filling. , For topping, cut butter into flour and sugar; stir in nuts. Sprinkle over tops. Bake at 350° until golden brown, 40-45 minutes.