Place oven mitts on.
Place a candy thermometer in the sauce pan.
Heat the sugar, corn syrup and water until dissolved in a heavy sauce pan.
As soon as it starts to boil, add the butter and stir constantly.
When the temperature reaches 230 degrees, add the nut of choice, stirring constantly.
Quickly remove from the heat at 305º (which is hard crack) and very quickly stir in the baking soda.
Using an offset spatula, quickly spread the mixture evenly onto a lightly oiled marble or granite slab.
Let cool completely for a couple of hours.
Using a Chef’s knife break brittle into small pieces.
Place in decorative tins.
Brittle keeps for 2 weeks at room temperature.