Pistachio-Cardamom Cupcakes with Dark Chocolate Ganache

Preheat the oven to 350°F. Line the wells of a 12-cup muffin pan and 6-cup muffin pan with papers, and grease the inside of the papers., To make the cupcakes: Place the pistachio nuts in the bowl of a food processor with half the flour. Process for 1 minute, until the nuts are finely ground. Sift the mixture through a strainer, returning any larger chunks to the machine for further grinding with the remainder of the flour., Whisk the ground nut/flour mixture with the cardamom, baking powder, and salt. Set it aside., In a large mixing bowl, beat the sugar, butter, and lemon zest until light and fluffy, 2 to 3 minutes. With the machine running, add the eggs one at a time, mixing until each egg disappears into the batter before adding the next. Scrape down the sides and bottom of the bowl., Add the sour cream and vanilla, mixing on low for 2 minutes, until the batter is uniform. Add the flour mixture and mix on low until just incorporated. Scrape the bowl one more time to make sure everything is evenly mixed., Scoop the batter by the scant 1/4-cup into the prepared cupcake pan, filling each well 2/3 full., Bake the cupcakes for 20 to 22 minutes, until a tester inserted in the middle of one of the center cupcakes comes out clean. Remove them from the oven and place them on a rack to cool., To make the ganache: Place the chocolate in a medium-sized heatproof bowl. Set the bowl aside., In a saucepan set over medium heat, bring the cream to a simmer. Pour it over the chocolate. Let stand for 3 to 4 minutes, to give the chocolate time to melt. Stir until the mixture is smooth, then add the butter and whisk until completely smooth and shiny., Run a spatula around the sides and bottom of the bowl to make sure no chocolate has settled there, add the salt, and stir until thoroughly combined., To assemble the cupcakes: Using a small offset spatula (or butter knife), place a large dollop (about 2 tablespoons) of ganache on each cupcake and smooth over in a circular motion from the center to the outer edges. For decoration, top each cupcake with chopped pistachios.