Melt chocolate and butter together in microwave or double boiler until smooth

Whisk whole eggs, egg yolks, and sugar until thick and pale

Fold melted chocolate mixture into egg mixture

Sift in flour and salt, fold gently until just combined

Grease 4 ramekins, divide mixture evenly between them

Place ramekins in slow cooker, add hot water halfway up sides

Cover and cook on high for 1-2 hours until edges are set but centers jiggle slightly

Cool for 2 minutes, run knife around edges and invert onto plates, serve immediately with ice cream