Preheat oven at 180°C/350°F. Grease and flour a 22x22cm/9x9-inch baking tray, or line it with parchment paper.
Melt chocolate and butter together in a bain-marie. Beat eggs and sugar until creamy. Add flour and beat for 1-2 more minutes. Add pecans and then the melted chocolate and butter mixture. Mix to combine.
Pour into the prepared pan and bake for about 30 minutes, or until a toothpick inserted in the center comes out almost clean.