Preheat your oven to 350°F (175°C) and grease a 9x13-inch baking dish with nonstick spray.

In a large bowl, cream together softened butter and sugar until light and fluffy. Add one egg and mix until combined. Stir in flour and baking powder, then spread the crust in the bottom of the prepared baking dish.

In another bowl, beat cream cheese and sugar until smooth. Add the eggs one at a time, blending well after each. Fold in chopped pistachios.

Pour the filling over the crust, smoothing it out evenly.

Bake for 40-45 minutes until the top is golden brown and the center remains gooey.

Allow to cool for about 15 minutes before slicing into squares and serving warm.