Preheat your oven to 350°F (175°C). Blend together crushed pistachios, grated Parmesan, melted butter, salt, and pepper until crumbly. Press into bottom of a greased springform pan and bake for 10 minutes. Let cool.

Heat olive oil in a skillet. Sauté chopped mushrooms for 5-7 minutes until golden brown. Season with salt and pepper and let cool.

In a bowl, beat cream cheese until smooth. Mix in sour cream, then add eggs one at a time, mixing well after each.

Fold sautéed mushrooms and feta into filling gently. Avoid overmixing.

Pour filling over crust and bake for 45-50 minutes until edges are set. Center should be slightly jiggly.

Cool in oven for 10-15 minutes with the door ajar. Transfer to refrigerator for at least 4 hours or overnight before serving.