Place pistachios, oats, flour, salt and soda in your food processor or Vitamix. Pulse several times until pistachios are broken down but still visible.

In a medium bowl, use an electric mixer to beat butter and sugars until light and fluffy; about 5 minutes. Slowly add in nut mixture and mix on low speed until just incorporated. Turn dough out onto parchment paper and finish mixing by hand.

Divide dough into two equal pieces. Shape into 2 logs about 1 1/2-inches in diameter. Wrap each in parchment paper and chill until firm, at least 1 hour or up to 5 days in advance.

Preheat oven to 350 degrees. Line two baking sheets with parchment paper. Slice dough logs into 1/4-inch thick slices; spaced about 1/2-inch apart. Bake 9-10 minutes until barely golden. Allow to cool 10 minutes before serving.