Process biscuits until finely crushed, add almonds and butter and mix until combined. Press over base of prepared tin. Refrigerate while preparing filling.
For filling, beat cream cheese with an electric mixer until smooth. Add eggs one at a time, beating well after each addition. Add sugar, sherry and flour, beat until smooth. While still beating, add cooled melted chocolate in a thin stream; beat until combined.
Scatter blackberries/boysenberries over the bottom of the crust then pour the filling over the top of the berries.
Cook in oven for about 50 minutes, or until firm to touch. Cool in oven with door ajar.
Remove cheesecake from tin. Serve with whipped cream and extra berries.