2. Make the Crust Mixture
In a medium bowl, combine the pistachios, lemon zest, chives, thyme, and two pinches of the salt. Stir well to combine. Add the butter pieces and stir with a fork, pastry cutter, or your fingers until the butter is evenly incorporated with the nuts and herbs.
Fold two pieces of wax or parchment paper into envelopes measuring about the same size as the halibut fillets: first fold in half, then fold in the sides. Open the envelopes and add half of the butter mixture to each envelope. Cover and seal the butter.