Beat the softened butter with both sugars for 3 minutes until pale and noticeably lighter in texture.

Beat in the eggs one at a time, then the vanilla.

Fold in the flour, baking soda and salt until barely combined, then the chopped chocolate. Do not overmix.

Chill the dough at least 1 hour, ideally overnight. Skip this and they spread into thin wafers.

Heat the oven to 180C / 160C fan. Scoop golf-ball portions onto a lined tray, well spaced.

Bake 10-12 minutes. Pull them when the edges are set but the centres still look underdone — they finish on the hot tray, and this is the single most common mistake.