Panettone is not sponge, it is a yeast cake with added egg yolks. The yolks give it its lovely yellow colour, and greatly retard the yeast's action, giving the cake its characteristic light texture. They are difficult to make and will usually be made by specialist firms in Italy, often family firms
A real Italian panettone is a subtle, flavoursome delight, and goes well with coffee, tea, brandy or grappa. I prefer it to the stodgy, over-sweet, over-heavy, calorie-laden, indigestion-causing Christmas cake and pudding so loved in this country.