Preheat your oven to 350°F (177°C). Grease and flour two 8-inch round cake pans.
In a food processor or blender, pulse the pistachios until finely ground.
In a mixing bowl, whisk together the ground pistachios, flour, baking powder, and salt. Set aside.
In a separate mixing bowl, cream together the softened butter and granulated sugar until light and fluffy.
Beat in the eggs, one at a time, followed by the vanilla extract.
Gradually add the dry ingredients to the wet ingredients, alternating with the milk, beginning and ending with the dry ingredients. Mix until just combined.
Divide the batter evenly between the prepared cake pans.
Bake for 22-25 minutes, or until a toothpick inserted into the center of the cakes comes out clean.
Remove cakes from the oven and let cool in pans for 10 minutes. Then transfer to wire racks to cool completely.
For the Rosewater Buttercream:
In a large mixing bowl, beat the softened butter until smooth.
Gradually add the powdered sugar, one cup at a time, beating well after each addition.
Add milk, one tablespoon at a time, until the desired consistency is reached.
Mix in the rosewater and pink food coloring, if using, until evenly incorporated.
Assembly:
Place one cake layer on a serving plate. Spread a layer of rosewater buttercream over the top.
Place the second cake layer on top and frost the top and sides of the cake with the remaining buttercream.
Optional: Garnish the cake with crushed pistachios and edible rose petals for a beautiful presentation.
Indulge in the heavenly combination of pistachio and rosewater flavors with every bite of this Fluffy Pistachio Cake with Rosewater Buttercream! 
