Wash and hull strawberries. Reserve half a dozen strawberries for garnish. Puree half of the remaining strawberries and set aside. Slice remaining strawberries in half and sweeten with 1/4 cup sugar and set aside.
In a medium saucepan thoroughly mix together 6 tablespoons of sugar, 1 1/2 tablespoons cornstarch, 1 tablespoon lemon juice, and a dash of salt. Stir in pureed strawberries. Cook over low heat, stirring constantly, until the mixture is thickened and clear. Let cool.
Beat 1/2 cup of the heavy whipping cream until stiff peaks form. Fold the whipped cream, 3 drops of red food coloring and if you want 2 tablespoons of port or sherry into the cooled strawberry mixture.
To assemble trifle, place half of the cake cubes in a layer on the bottom of a trifle bowl. Sprinkle cake with 2 tablespoons of port or sherry. Spoon half of the sliced strawberries on the cake. Spoon 1/2 of the strawberry cream mixture over the sliced strawberries. Repeat with the remaining cake, strawberries and cream mixture.
Cover and refrigerate for three and a half hours. Shortly before serving, whip the remaining heavy cream or use strawberry Cool Whip to garnish the top of the trifle along with the reserved whole strawberries and sprigs of mint.