Prep time INCLUDES 45 min of chilling time. True shortbread should only have 3 ingredients: sugar, butter, oat flour so you can omit the rest of the ingredients if you like. You can use any type of flour here (try almond for gluten-free shortbread). If you don't have caster (superfine) sugar, use powdered or regular cane sugar but make sure you cream the sugar in butter until it is no longer granular. The key is to coat every flour particle with fat so that gluten can't form, resulting in crumbly texture. ALWAYS use regular full fat stick butter. Margarine will not yield the same texture. This would make an amazing crust for cheesecake or served with ice cream and strawberries.