Preheat oven to 350 degrees. Toast pecans on a baking sheet for approximately 5-10 minutes. Let nuts cool and measure them out so they are ready to go when you need them. It's important to plan and measure everything in advance because once you start boiling the sugar mixture, you won't have time later. You can also use almonds but everyone thinks the pecans taste better.
Lightly oil a 15 1/2 in. by 10 1/2 in. metal baking pan. I use Pam and then wipe off the excess with a paper towel. You should also spray a spatula for later and set it aside.
Cut butter into small pieces and in a 2-3 quart heavy sauce pan combine with the sugar, light corn syrup and water. Bring mixture to a boil over moderately high heat, stirring until sugar is dissolved. Boil sirring occasionally until candy thermometer registers 290 degrees. It takes approximately 10 minutes and the mixture will start to turn a caramel color. It's very important that you let it reach the "hard crack" stage. If you don't, the toffee will be chewy instead of crunchy.
Once the mixture is the desired temperature, quickly stir in the 2 1/4 chopped pecans and immediately pour out onto the prepared baking sheet. Using a spatula, quickly spread the toffee into as even a layer and as close to the edges of pan as possible.
Let mixture stand 1 minute. The original recipe says you can just melt 12 oz. of chocolate chips over the hot mixture and spread them with a spatula but I prefer to melt baking chocolate in a double boiler and spread that over the sugar mixture. I also wipe off the top of the sugar mixture with a paper towel so the chocolate will adhere and not separate after it's cooled. Then sprinkle 1 cup of finely chopped pecans on top and gently press them into the chocolate.
Chill the toffee until the chocolate is firm, at least 2 hours. I usually chill it overnight. Once cooled, break toffee into bite size pieces and pack them into bags and boxes. Keep toffee chilled to prevent the chocolate from melting. Then enjoy!