In a small saucepan over high heat, combine the spiced wine and 1/2 cup sugar and simmer until slightly thickened. Reduce the heat to medium and cook until the contents become a thick spiced wine reduction. Set aside. 

In a heavy 1-quart saucepan, heat 3/4 cup of the cream until hot. In a metal bowl, whisk together the egg yolks, 3 tablespoons sugar and salt until well combined, then add the hot cream in a slow stream, whisking until combined. Transfer the mixture back to the saucepan and cook over medium-low heat, stirring constantly, until it registers 160°F on a thermometer. Pour the custard through a fine-mesh sieve into a bowl and stir in the vanilla.

In a double boiler or in a metal bowl set over a saucepan of simmering water, melt the chocolate, stirring frequently. Alternatively, melt the chocolate in a glass bowl in a microwave at 50 percent power for 3 to 5 minutes. Stir the espresso powder into the chocolate, then whisk in the custard and the spiced wine reduction until smooth. Let cool.

In a bowl, using an electric mixer, beat the remaining 1 1/4 cups cream until it just holds stiff peaks. Whisk one-fourth of the whipped cream into the chocolate custard to lighten, then gently but thoroughly fold in the remaining whipped cream.

Spoon the mousse into eight 6-ounce stemmed glasses or ramekins, cover and refrigerate for at least 6 hours or up to 1 day. Let stand at room temperature for about 20 minutes before serving.

NOTE: To vary the flavor, you can replace the 1 teaspoon vanilla extract with 3 tablespoons Grand Marnier or 2 tablespoons Cognac, whisked into the strained custard.