In a small saucepan, melt the butter and set aside. Blend pistachios into flour, do not overblend it will turn into a paste. Sift out the chunks until you're left with 30 grams of finely ground pistachio.
In a large bowl, beat the eggs and both sugars at high speed until the mixture is thick, about 5-8 mins. Stir in the vanilla and orange zest.
Sift in the flour, pistachios, baking powder, salt, and cardamom powder. Gently fold in, do not over mix.
Slowly pour the melted butter into the flour mixture, and gently fold until combined. Cover and refrigerate for at least 1 hour or overnight.
Preheat your oven to 375F. Grease the molds of your Madeleine pans with melted butter. Then dust with flour and tap out the excess flour.
Drop a heaping tablespoon of the batter into the center of each prepared mold, leaving the batter mounded in the center.
Bake the Madeleines for about 8 to 11 minutes, until the edges are golden brown and the centers spring back when lightly touched.
Remove the pans from the oven and immediately remove from the mold. Place Madeleines on a wire rack to cool.
Melt the chocolate chips and mix in the oil, until smooth. Dip the madeleines, allow the chocolate to harden, and enjoy with a cup of tea!