How to Make It
Melt the butter in a saucepan over medium-high heat and cook, stirring constantly, until golden brown, 3 to 4 minutes. Reserve 1 cup of the melted butter in a heat-proof container and set aside until lukewarm; discard the rest.
Heat the oven to 350º F. Spray a 9”-round cake pan with nonstick spray and line the bottom with parchment paper.
Place 1¼ cups of pistachios in the bowl of a food processor and process until finely ground.
Whisk the egg whites and vanilla in a small bowl and set aside. Sift the sugar into a large mixing bowl, then stir in the flour, ground pistachios, and salt. Combine the egg mixture and the flour mixture and stir until just combined. Stir in the reserved melted butter.
Pour the batter into the prepared pan and bake until a small knife inserted into the center comes out clean, about 50 minutes. Let cake cool to room temperature before removing it from the pan.
Before serving, mix the remaining ½ cup pistachios with the honey and pile them on top of the cake.