Let me start off by saying that this frosting is not quick and easy. It is luscious, creamy, delicious, and once you taste it, you will never want that butter and confectioner sugar icing ever, ever again. Julia says that you can do this by hand, but I wouldn't recommend it. All you need is a hand mixer to make this successfully. Don't be afraid--it may sound intimidating, but it's really pretty easy.
For about 2 cups (enough to fill & frost a 9" cake)
2/3 cup sugar and 3 tbl water in a small saucepan with cover
1 egg and 3 yolks in a stainless saucepan
2 sticks soft, unsalted butter
1 tsp vanilla extract
2-4 oz melted chocolate
Beat the egg yolks in the saucepan until they thicken and lighten in color.
Shaking pan gently by handle, bring sugar & water to boil over high heat; when liquid is perfectly clear, cover for a minute, until bubbles have begun to thicken. Uncover, and boil to the soft-ball stage, 238 degrees.
Immediately, begin beating hot syrup into egg yolks, being careful not to hit the beaters with the syrup (You can do this in a blender if you prefer.).
Set the pan over barely simmering water, and beat slowly until the mixture is too hot for your finger, and has thickened enough to form a fat ribbon when lifted. Remove from heat and beat over cold water until cool. Beat in the butter by 2 tbl bits, add the vanilla and the chocolate. Beat over ice until of spreading consistency.