Preheat your oven to 400 degrees and line a 12 cup muffin tin with muffin liners.
Place the butter In a large microwave safe mixing bowl. Microwave the butter in 20 second bursts, stirring after every burst until it is melted.
Use a wire whisk to mix together the butter and the sugar. Whisk this for about a minute or until the sugar is dissolved.
Add the eggs and vanilla, continuing to whisk until the ingredients are fully combined.
Add the pistachio pudding mix, along with the baking powder, salt, and the mix. Whisk the mixture again.
Add the flour and whisk it again, just until the flour is incorporated. Do not over mix or your muffins will be tough.
Spoon the batter into the muffin cups, filling them until they are about ⅔ full.
Sprinkle the ¼ cup sugar on top of the muffin batter, dividing it equally between each muffin cup.
Bake the muffins in the hot oven for about 8 minutes and then reduce the heat in the oven to 350 degrees. Bake for 10 to 12 more minutes or until the tops of the muffins are golden brown and spring back when touched lightly.
Take the muffins out of the oven and put them on a wire rack to cool.
Serve the muffins warm or at room temperature.
Store muffins in a tightly sealed zip top bag at room temperature for up to 3 days.