This is a treat for the eyes as well as the palate and keeps for several days once refrigerated.
Line a square 8 – inch mold with parchment paper.
Heat the oven to 350 °F. Spread the pistachos on a baking sheet and grill for 2 to 3 minutes.
Allow the pistachios to cool and chop roughly. If you wish, set aside 2 Tbsp more finely ground pistachios to garnish.
Pour 2/3 of condensed milk into a small pan. Add the dark chocolate and cardamom then heat on medium-low. Mix gently until the chocolate is completely melted. Add pistachios and mix well.
Pour the mixture into the mold and separate evenly using a spatula.
Pour the remaining condensed milk into a small pand then add the white chocolate and vanilla extract. Heat on medium-low. Mix gently until the chocolate is completely melted.
Pour the mixture onto a layer of dark chocolate and spread with a spatula.
Decorate with the remaining pistachios and a pinch of fleur de sel.
Refrigerate for at least 2 hours before serving.