Line a large baking sheet with parchment paper.
In a large bowl, beat butter until soft. Add sugar and beat until light-colored and fluffy.
Add eggs, one at a time, beating between each addition.
Combine flour, baking soda and salt in separate bowl.
On low speed, gradually add flour mixture to butter mixture just until combined. Do not over mix.
Stir in pistachios and white chocolate.
Divide dough in half. With your hands, shape each half into a log about 12 inches long and 3 inches wide. They do not have to be perfect, as they will spread out as they cook.
Bake for approximately 35-45 minutes. Check for a nice golden top.
Remove from the oven and let cool about 15 minutes.
While still warm, carefully slice the loaves at an angle, in 1-inch increments, using a serrated knife.
Place sliced biscotti flat on a baking sheet and let cool completely. Some recipes call for putting them back in the oven to dry out and become crispy. I prefer a little give in my biscotti so usually eliminate this step.