How to Make It
Preheat the oven to 325°. Butter and flour a 9-inch cake pan. In a food processor, pulse the pistachios until finely chopped. In a medium bowl, whisk the 1 1/2 cups of flour with the baking powder and salt. In a large bowl, combine the 1 1/2 sticks of butter, 1 cup of the sugar, the pistachio paste and vanilla. Using a handheld electric mixer, beat at medium speed until fluffy, about 3 minutes. Beat in the eggs 1 at a time, then beat in the flour mixture at low speed just until incorporated. Fold in 1 cup of the chopped pistachios. Spread the batter in the prepared pan and bake for about 35 minutes, until a cake tester inserted in the center comes out clean. Transfer the cake to a rack to cool completely, about 2 hours.
In a small bowl, whisk the mascarpone with the sour cream, the remaining 1 teaspoon of sugar and the orange zest . Cut the pistachio cake into wedges and serve with a big dollop of the orange cream, candied orange and a drizzle of lavender honey. Garnish the slices with the remaining chopped pistachios and serve.
Pistachio paste is available at specialty food and baking supply shops, and from kingarthurflour.com.