Preheat the oven to 350° and line 2 baking sheets with parchment paper. In a standing electric mixer fitted with the paddle, beat the butter with the sugar at medium speed until creamy. Add the eggs, vanilla seeds and rum and beat until smooth. In a small bowl, whisk the flour with the cocoa powder, baking powder, salt and cinnamon. Add the dry ingredients to the batter and beat at low speed until incorporated. Beat in the whole pistachios.