A layer of fudge sauce (original recipe by Sara Perry from her book Deep, Dark Chocolate) sits beneath hot chocolate topped with whipped cream and shaved chocolate. The exciting part is when you spoon the fudge from the bottom of the glass. There is a grown up version involving spirits, which you can easily leave out.
Combine the chocolate and butter in a heavy-bottomed small saucepan and melt over very low heat, stirring until smooth. (So long as the heat is low, you do not need to use a double boiler method. If you have concerns about scorching the chocolate, set the saucepan in a skillet with 1 inch of water and bring to a simmer.)
Add the boiling water, sugar and corn syrup and stir to blend.
Raise the heat to medium-high. Once the sauce boils, do not stir, but monitor the heat to maintain a gentle boil. Cook the sauce uncovered until thickened like heavy cream, about 3 minutes.
Remove from the heat and let it cool for about 10 minutes. Add the salt and vanilla. Add the spirits, if using.
Fill each serving glass about 1/4 full with fudge sauce and let cool to room temperature. (Reserve the rest for ice cream).
When ready to serve, make 6 ounces of your favorite hot chocolate per serving. Go light on the chocolate for the best contrast. Pour the hot chocolate into the glass. Top with whipped cream and shaved chocolate before serving with a long spoon.
To make a light hot chocolate: Combine 1/4 cup granulated sugar with 1/4 cup good-quality cocoa powder. Add 3 cups hot milk and stir to blend.
To shave chocolate, rub a vegetable peeler over the edge of a chocolate bar over a piece of parchment paper until you've collected several tablespoons to sprinkle on to of the whipped cream.