01 - Preheat oven to 425°F (220°C). Grease 4 individual ramekins with butter and lightly dust with flour, tapping out any excess.
02 - In a food processor, process the pistachios until finely ground. Add heavy cream and blend until a thick, smooth paste forms. Set aside.
03 - In a heatproof bowl set over a pot of simmering water, melt the chocolate and butter together, stirring until glossy and smooth. Remove from heat and let cool slightly.
04 - In a separate bowl, whisk the eggs, egg yolks, and sugar until pale and slightly thickened.
05 - Pour the melted chocolate mixture into the egg mixture, whisking gently to combine. Sift in the flour and salt, and fold until just incorporated.
06 - Divide half the batter evenly among the 4 ramekins. Spoon a heaped teaspoon of pistachio paste into the center of each. Cover with the remaining batter.
07 - Bake for 11–13 minutes, until the tops are set but the centers are still soft.
08 - Immediately run a knife around the edges. Let rest for 1 minute, then invert onto plates. Sprinkle with chopped pistachios, dust with powdered sugar, and serve instantly with a scoop of vanilla ice cream if desired.