PREHEAT oven to 350°F. Microwave chocolate and butter in large microwaveable bowl on HIGH 2 min. or until butter is melted. Stir until chocolate is completely melted.
STIR in sugar until well blended. Add eggs, 1 at a time, beating with electric mixer on low speed after each addition until well blended. Stir in vanilla. Add 1/4 cup of the flour and the baking soda; mix well. Add remaining 1 cup flour alternately with the water, beating until well blended after each addition. Pour evenly into greased and floured 9-inch round cake pan.
BAKE 30 min. or until toothpick inserted in center comes out clean. Cool 10 min.; remove from pan. Cool completely on wire rack. Drizzle with Chocolate Glaze and top with berries just before serving.