01 - Preheat the oven to 425°F (220°C). Generously butter 4 individual ramekins and lightly dust with flour, tapping out any excess to ensure clean release.
02 - In a food processor, grind the shelled pistachios until finely milled. Add the heavy cream and blend until a thick, smooth paste forms. Set aside.
03 - Set a heatproof bowl over a pot of barely simmering water. Add the chopped bittersweet chocolate and butter, stirring gently until glossy and completely smooth. Remove from heat and let cool slightly.
04 - In a separate mixing bowl, whisk the whole eggs, egg yolks, and granulated sugar vigorously until the mixture turns pale and falls in thick ribbons.
05 - Pour the melted chocolate mixture into the egg mixture, whisking gently to combine. Sift in the flour and salt, then fold with a spatula until just incorporated—do not overmix.
06 - Divide half the batter evenly among the prepared ramekins. Spoon a heaped teaspoon of pistachio paste into the center of each, then cover with the remaining batter, smoothing the tops.
07 - Bake for 11 to 13 minutes, until the tops are just set but the centers still have a visible jiggle—this ensures a molten interior.
08 - Immediately run a thin knife around the edges of each ramekin. Let rest for 1 minute, then invert onto serving plates. Garnish with chopped pistachios, a dusting of powdered sugar, and a scoop of vanilla ice cream if desired. Serve immediately.