Preheat your oven to 375°F (190°C). Line the muffin tin with paper liners or grease it lightly.
In a large mixing bowl, whisk together the flour, sugar, baking powder, and salt until well combined.
In another bowl, mix together the milk, vegetable oil, eggs, and vanilla extract.
Pour the wet ingredients into the dry ingredients and stir until just combined. Do not over-mix; a few lumps are okay.
Gently fold in the chopped pistachios and white chocolate chips (if using) until evenly distributed.
Spoon the batter into the prepared muffin tin, filling each cup about ¾ full. If desired, sprinkle additional chopped pistachios on top for garnish.
Bake in the preheated oven for about 18-20 minutes, or until a toothpick inserted into the center comes out clean.
Once baked, let the muffins cool in the tin for 5 minutes, then remove them and place on a cooling rack to cool completely.