Lightly grease and/or line with parchment a loaf pan. If you are using a 9x5 loaf pan, the loaf will be a little flatter.
Preheat oven to 350°F
Pulse your unshelled pistachios in a food processor until they are finely chopped. I personally don't mind a few bigger chunks but MOST should be like a rough sand.
Combine flour, salt, and baking powder and pistachios in a bowl. Whisk to mix
Mix brown sugar with butter, either by hand or mixer. I used a hand mixer over a stand mixer. The sugar will look like wet sand.
Add in the egg to the sugar and butter and combine well.
Add in vanilla and oil to sugar mixture until homogenous.
Gently stir milk into wet ingredients until combined.
Fold in your flour pistachio mixture into the wet mix with a spatula. Mix until just combined, no dry flour remaining. Do not overmix. Your batter will most likely not be smooth, depending on how finely chopped your nuts are.
Chop your chocolate to your desired level and fold into batter.
Pour batter into prepared loaf pan and bake on center rack for 50-70 minutes. Check loaf with toothpick starting at 50 minutes. Bake time is going to vary depending on pan size and color. It may bake closer to 50 minutes in a 9x5 pan and closer to 70 minutes in an 8x4 pan. Bread is done when toothpick comes out cleanly. Let bread cool in loaf pan for about 10 minutes before removing and letting cool on a wire rack.
While your bread is cooling, melt your chocolate and then drizzle over top of bread. You can also add additional chopped pistachios on top for added crunch. Enjoy!
