Method

• Beat butter and both sugars until pale and fluffy, 2 minutes. Add egg, yolk and vanilla; beat to combine.
• Sift in flour, bicarb and salt. Fold until just combined. Fold in chopped chocolate.
• Chill dough at least 30 minutes (overnight is better).
• Preheat oven to 180°C fan-forced. Line 2 trays with baking paper.
• Scoop heaped tablespoons of dough, roll into balls (about 50g each). Place well apart on trays - they spread.
• Bake 10-12 min until edges are golden but centres still look slightly underdone.
• Immediately sprinkle sea salt flakes on top. Cool on the tray 5 min before transferring to a rack.
• Eat warm. Keep for 4 days in an airtight container.