Line an 11x7-inch pan with well-greased wax or parchment paper. Set aside.
Melt the butter on low in a heavy saucepan. Stir in the sugar, syrup and water. Stirring constantly, use a candy thermometer and cook until the mixture reaches 305 degrees F.
Pour the hot candy onto the prepared pan. Spread the mixture to the edges. Allow to sit until the mixture is stable but still hot. Spread the melted chocolate chips over the top. Sprinkle nuts over the top of the chocolate and gently press in.
Allow the candy to cool and harden. Break into pieces and store in an airtight container.
Notes
To melt chocolate chips, put in pyrex and microwave. Stir every 30 seconds until smooth.
I suggest you read through the post before making this recipe for any potential problems you may have -- with butter separating during the cooking process or with the chocolate separating from the toffee.