01 - Preheat oven to 425°F (220°C). Grease 4 individual ramekins (6-8 oz) with butter, dust lightly with flour, and tap out any excess.
02 - Process the shelled pistachios in a food processor until finely ground. Add the heavy cream and blend until a thick, smooth paste forms. Set aside.
03 - Set a heatproof bowl over a pot of simmering water. Melt the chopped 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 granulated sugar together until the mixture turns pale and slightly thickened.
05 - Pour the melted chocolate mixture into the egg mixture, whisking gently to combine. Sift in the flour and salt, then fold until just incorporated. Do not overmix.
06 - Divide half the batter evenly among the 4 prepared ramekins. Spoon a heaping teaspoon of pistachio paste into the center of each ramekin, then cover with the remaining batter.
07 - Bake for 11 to 13 minutes, until the tops are set but the centers still feel soft to the touch.
08 - Immediately run a knife around the edges of each ramekin. Let rest for 1 minute, then invert onto serving plates. Sprinkle with chopped pistachios, dust with powdered sugar, and serve right away with a scoop of vanilla ice cream if desired.