Preheat your oven to 425°F (220°C) and grease four ramekins with unsalted butter, dusting them with flour.

In a microwave-safe bowl, melt the unsalted butter and semi-sweet chocolate together in 30-second intervals, stirring until smooth.

In a separate bowl, whisk together the granulated sugar, brown sugar, eggs, egg yolks, vanilla extract, and salt until slightly frothy.

Pour the melted chocolate mixture into the egg mixture slowly, stirring continuously until smooth.

Gently fold in the all-purpose flour, being careful not to overmix, to create a light batter.

Stir in the chopped pistachios until evenly distributed throughout the batter.

Fill the prepared ramekins about three-quarters full with batter and gently shake to settle it.

Bake for 12-14 minutes, until edges are firm but centers jiggle slightly for that molten core.

Let the ramekins cool for 3-5 minutes before serving to help them set.