1Preheat your oven to 200°C (392°F).
Crush the Oreo cookies into fine crumbs using a food processor or by placing them in a sealed bag and crushing with a rolling pin.
Melt the dark chocolate and butter together in a heatproof bowl over a pot of simmering water, stirring until smooth.
In a separate bowl, beat the eggs and sugar together until the mixture becomes pale and slightly thickened.
Gently fold the melted chocolate and butter mixture into the egg and sugar mixture.
Add the crushed Oreo cookies to the mixture and stir until well combined.
Grease small ramekins or muffin tins with butter and dust with cocoa powder to prevent sticking.
Pour the batter into the prepared ramekins, filling them about three-quarters full.
Bake in the preheated oven for 10-12 minutes, or until the edges are firm but the center is still soft.
Remove from the oven and let them cool for a minute before carefully inverting onto a plate.
Serve immediately while the center is still gooey, optionally with a scoop of vanilla ice cream or a dusting of powdered sugar.