Mahnke Family Recipes- River Cottage Shortbread

Ingredients

• 1 ⁄ 2 lbs / 175 g butter - softened
• 1 ⁄ 4 lbs / 90 g caster sugar - plus extra for sprinkling
• 2 medium egg yolks
• 1 ⁄ 2 lbs / 200 g plain flour - plus extra for dusting
• 1 large pinch salt
• 1 whole grated zest of an orange or lemon