Preheat the oven to 180ºC . Butter an 20 cm square cake pan. Line the pan with wax paper. Butter the paper; flour the pan. Melt the chocolate in the top of a double boiler over hot water until smooth. Remove from heat. Beat the butter in a large bowl until light. Beat in the vanilla, both sugars and the corn syrup. Add the eggs, one at a time, beating thoroughly after each addition. Slowly beat in the melted chocolate, the flour, the salt and 1 cup pecans. Spoon the batter into the prepared pan. Sprinkle the remaining half cup pecans over the top. Bake until a toothpick inserted in the centre comes out fairly clean, about 1 hour. Cool in the pan on a wire rack 30 minutes. Cover the pan with another rack and invert. Remove the pan and peel off the paper. Invert back onto a wire rack and let stand until completely cool. Chill the brownie cake for about 30 minutes before cutting into bars. MAKES ABOUT 24 BROWNIES