On medium heat, combine the cocoa, sugar and olive oil in a small pot. Heat until the mixture just begins to bubble, stirring continuously, about 3 min. Remove from the heat and let cool 5 min. Stir in the flour and vanilla. Add the egg yolks one at a time, mixing well after each addition.
Beat the egg whites until soft peaks form. Gradually fold the chocolate mixture by thirds into the egg whites. Pout into the prepared cake pan. Bake 18 to 22 minutes or until the edges of the cake pull away from the sides and the top has firmed up. Remove cake from oven and gently loosen the cake from the sides of the pan using a table knife. Cool completely in the pan on a wire rack. Remove from pan and place on a serving plate. Cover and chill for at least 6 hours.
Uncover cake and cut into 8 wedges. Place each wedge on a dessert plate and heap with berries. Drizzle with about 1&1/2 tsp. balsamic vinegar. Add a spoonful of whipped cream if desired.
*This cake works with Lime, Lemon or Blood Orange Olive Oil.
