Preheat oven to 170 degrees Celsius (fan forced). Line a square cake tin (or a square 8 x 8 pan) with baking paper.
Mix the flour, cocoa powder, baking powder and sea salt in a bowl. Set aside.
In the top of a double boiler or in a heatproof bowl over barely simmering water, melt the chocolate bar and butter, stirring occasionally until smooth. Cool to room temperature.
In a large mixing bowl, beat the eggs and sugar until combined. Add in the chocolate mixture to the egg mixture.
Gently add in the flour mixture into the chocolate-egg mixture and combine thoroughly. Add in the chocolate chips.
Pour the batter into the cake tin and bake for 45 - 50 minutes or until a wooden skewer comes out clean.
Remove from oven and let cool in cake tin for 5 minutes before turning over. Cool completely before cutting into squares.