Preheat your oven to 350°F (175°C) and prepare a 9-inch round cake pan by greasing it and lining the bottom with parchment paper.
In a large mixing bowl, cream together the melted butter and granulated sugar until light and fluffy.
Add the eggs one at a time, beating well after each addition to ensure they are fully incorporated.
Mix in the rosewater until well combined.
In a separate bowl, combine the all-purpose flour, baking powder, and salt.
Gradually add the dry mixture to the wet ingredients, alternating with the whole milk, starting and ending with the flour mixture.
Fold in the chopped pistachios carefully using a spatula.
Pour the batter into the prepared cake pan and smooth the top with a spatula.
Bake in the preheated oven for 30-35 minutes, or until a toothpick inserted into the center comes out clean.
Allow the cake to cool in the pan for 10 minutes, then transfer it to a wire rack to cool completely.
Once cooled, dust the top with powdered sugar if desired and garnish with extra pistachios before serving.