Place 1 cup sugar and 1 cup butter in a quart saucepan with 3 tablespoons water. Heat stirring until butter has melted. Cook and stir constantly until mixture bubbles up thick and turns amber in color. This will require approximately 10 minutes or more. Add 1 teaspoon vanilla and pour in a thin layer in a buttered pan. Lay 3 sweet chocolate bars on this hot candy. Spread evenly over toffee and sprinkle 3/4 cup ground pecans over chocolate. When cold, break into pieces. Candy should be done when candy thermometer reaches 320 degrees.