In a small saucepan on low heat, melt the butter and chocolate chips.
Remove from the heat and stir in honey, vanilla and salt.
While the chocolate mixture cools, blend one cup of the pistachios in a powerful blender (Blendtec or Vitamix) until you have pistachio butter. Try to stop blending just when it turns into a paste and before too much oil is released. If you do not have a powerful blender , you can use a food processor and process until you get a fine powder. The resulting brownie will not be fudgy, but more cakey, with pistachio morsels. Fret not, it will still be delicious!
Mix the eggs and baking powder into the cooled melted chocolate, then add in the pistachio butter.
Transfer this mixture to a buttered 8" square baking dish.
Bake for 30 minutes or until a toothpick inserted into the center of the brownies comes out clean.
Chop the remaining one cup of pistachios and sprinkle over the top of the brownies.
Cool to room temperature before cutting and serving.