Preheat your oven: Set your oven to 180°C (350°F) and line two baking trays with parchment paper. This preparation step is crucial as it helps in even baking.
Cream the butter and sugar: In a mixing bowl, take 100g of softened butter and 75g of caster sugar. Using an electric mixer, cream them together until the mixture is light and fluffy, which should take about 3-5 minutes.
Combine dry ingredients: Gradually add 225g of plain flour and the zest from 2 oranges to the butter mixture. Mix until everything is just combined. Be careful not to over-mix, as this can result in tough biscuits.
Add wet ingredients: Crack 1 egg into the mixture along with 1 tablespoon of orange juice. Stir until a soft dough forms. The dough should be slightly sticky but manageable.
Shape the biscuits: Take small portions of the dough and roll them into walnut-sized balls. Place them on the prepared trays, making sure to leave enough space between each ball as they will spread while baking.
Flatten the dough: Gently press each dough ball down with your fingers or the palm of your hand to create a flat disc shape.
Chill the dough: Place the trays in the refrigerator for 15 minutes. Chilling helps firms up the dough, giving it a better shape during baking.
Bake: After chilling, put the trays in the oven and bake for 12 minutes, or until the edges turn golden brown. Keep an eye on them to prevent over-baking.
Cool: Once baked, remove the trays from the oven and let the biscuits cool on the trays for a few minutes before transferring them to a wire rack to cool completely.