Preheat oven to 200 degrees C. Place butter and sugar into stand mixer with paddle attachment. Mix on high speed to cream butter and sugar together, without aerating mixture. Add the egg and mix on high speed until combined. Reduce the speed to low, add the flour and mix until dough comes together.
Turn out onto a sheet of baking paper then place another sheet of baking paper on top. Roll out dough to 2mm thickness then place in freezer for 5 mins to chill. Remove from freezer then carefully place pastry into greased tart tin. Place baking paper then baking weights on top of pastry. Bake for 10 mins before removing paper and weights. Return to oven and cook until golden - about 10 more mins. Remove from oven and set aside to cool.