In large bowl, stir together chocolate and butter until completely melted.

Whisk eggs and sugar above at simmering water until sugar completely dissolved.

Use hand mixer and beat eggs with sugar for 2-3 minutes until pale and fluffy.

Beat in vanila and salt then stir in warm chocolate mixture until evenly blended. Stir in flour and fold it in until well incorporated and smooth. Fold in chocolate chips.

Pour batter into prepared square pan 20 cm. Sprinkle chocolate chips on top. Bake until slightly puffed, about 17-20 minutes.