Frosting for Chocolate Cookies

This is an uncooked frosting: the egg white is stirred into sugar and chocolate and spread straight onto cookies, with no cooking step at any point. The notes below explain the terms and why the method is no longer used.

• The egg white is never cookedNothing in the method brings the white to a temperature that would kill Salmonella. The residual heat of a cookie coming off the sheet warms the sugar enough to make it spread, but it does not hold the thin film of icing at a lethal temperature for any meaningful time, and the icing cools within a minute or two.
• Sugar is not a safeguard hereVery high sugar concentrations slow bacterial growth but do not sterilise, and two teaspoons of cream plus a raw white lowers the concentration further. The frosting also sits at room temperature on the cookies for as long as they last.
• Who is most at riskUncooked egg-white frostings are a recognised vehicle for raw-egg illness, and the setting this recipe imagines is exactly the vulnerable one: a plate of cookies handed round to children, older guests and anyone pregnant or immunocompromised. Use a current cooked-frosting or meringue-powder recipe instead.
• "2 squares melted chocolate"A square is one ounce of unsweetened baking chocolate, so 2 oz in total. Unsweetened is what the period meant unless it said otherwise; semi-sweet would throw the sugar balance well off.
• Powdered sugarConfectioners' sugar, in practice the 10X grade sold today. It contains a small amount of cornstarch as an anti-caking agent.
• "Cream to moisten"The two teaspoons are a starting point, not a fixed quantity — the working consistency depended on how much liquid the egg white supplied that day. Recipes of this era routinely left the final liquid to the cook's judgement.