The Pistachio Brittle

For the most recent underground dinner, we had a dessert involving poached pears, some blue cheese and pistachio brittle. Why pistachio brittle? you might ask. Simply because we had some pistachios and I thought they would go better with the pears than traditional peanut brittle would. And by all accounts it did!
Ingredients
2 cups sugar
1 cup light corn syrup
1/2 cup water
1 cup butter - preferably unsalted, chopped into small cubes
2 - 3 cups shelled, roasted, salted pistachios
1 t baking soda (bicarbonate of soda)

Method
In a straight sided pan with a candy thermometer clipped to the side, place the sugar, water and corn syrup. Bring to the boil, stirring frequently over a medium flame. It should rwach a full, rolling boil after about 10-15 minutes.Add the butter and cover the pan for a couple of minutes. The thermometer will be in the way, so do the best you can.
Put a "flame tamer" under the pan (or a cast iron pan) such that the heat is properly diffused, preventing any hot spots in the pan. Cook and stir the mixture until it reaches about 280F. Be very careful that you o not get any of this mixture on yourself during the process. It retains heat and sticks as well.
Add the pistachios and stir to incorporate. Continue to heat until the temperature reaches 305F. You should stir the nisxture the whole time. By adding the nuts while the caramel is a bit cooler gives the mixture a bit of a chance to toast the nuts for extra flavor.
Once it has reached 305F, stir in the baking soda and stir. The mixture will foam up, so be careful.
Pour into a greased baking sheet, smooth into the corners with a palette knife and allow to cool.