We coated our butter crunch with a layer of melted chocolate. You can leave the candy covered and simply cut it into squares or break it into pieces when cool.
Butter a 9-inch square baking pan, and line the bottom with a piece of parchment paper that extends up and over two sides. Butter the parchment, and set the pan aside.
Place the butter and water in a large saucepan. Cook over medium-high heat until the butter is melted. Add the sugar, and stir constantly until dissolved and the mixture comes to a boil. Using a pastry brush dipped in water, brush away any sugar crystals on the side of the pan to prevent recrystallization. Cook until the mixture is dark amber in color. Remove from heat, and stir in the pecans. Pour into the prepared baking pan, and let stand at room temperature to cool completely.
Place the chocolate and corn syrup, if using, in a small heat-proof bowl set over a pan of barely simmering water. Stir occasionally until combined and completely melted. Let cool slightly, and spread over the top of the cooled toffee. Arrange the pecan halves on top, and let sit at room temperature until the chocolate has cooled completely and set, at least 2 hours or overnight. Carefully unmold by lifting out the parchment paper. Break or cut into pieces, and store in an airtight container at room temperature for up to 1 month.