This lovely frosted pistachio cake makes the perfect baking project for an autumn weekend! Héloïse Brion shares the recipe from her new book, My Art of Entertaining Serves 10. Total preparation time (including cooling and chilling): 1½-2 hours. For the cake Butter and flour, for greasing  2 cups (9 oz./250 g) shelled pistachios 2¼ cups (10 oz./280 g) all-purpose flour 1 scant tbsp (11 g) baking powder 2 pinches baking soda 1 generous pinch fleur de sel 1½ sticks (6 oz./180 g) unsalted butter, diced, at room temperature ¾ cup (5 oz./150 g) superfine sugar ⅔ cup (5¼ oz./150 g) brown sugar 4 egg whites …