Butter 2 (8-ounce) ovenproof ramekins, and then dust them with cocoa powder, shaking off any excess.
Melt the chocolate and butter together in a bowl over a pan of gently simmering water. While the chocolate is melting, use an electric whisk or a hand held mixer to beat together the eggs and sugar until pale and thick. Pour the melted chocolate into the egg mixture and gently fold in the flour. Spoon the pudding into the ramekins and bake for 10 minutes.
Serve the puddings in either the ramekins or turned out onto serving plates. Dust the puddings with cocoa powder and garnish with a dollop of creme fraiche.