I always use margarine, butter is too heavy. Eggs can vary a lot in size, for perfect results weigh the 3 eggs. This will more than likely weigh over or under 150g (6 oz). For example, if the eggs weigh 175g you would use 175g each of the flour, sugar and margarine.
I used this recipe for an entry for my local Horticultural Society Annual Show at the weekend. I dusted it with caster sugar instead of icing sugar and filled it with a good quality raspberry jam (as per WI standards). Pleasingly I attained a FIRST place for it, so thank you very much for this lovely recipe. This week I am going to make another one to fill with homemade blueberry jam. - 20 Aug 2012