• Preheat your oven to 325°F. Grease or line with parchment paper a standard 9-inch x 5-inch loaf pan and set it aside.
• In a small heat-safe bowl, place the chopped chocolate and melt in 30-second bursts in the microwave at 60% power until melted and smooth (or over a double boiler). Set the bowl aside to cool briefly. Into a medium-sized bowl, sift together the flour, xanthan gum, cornstarch, and cocoa powder, then add the salt and whisk to combine well. Set the bowl aside.
• In the bowl of a stand mixer fitted with the paddle attachment (or a large bowl with a hand mixer), beat the butter and sugar until the mixture falls from the beater in a ribbon when the paddle is lifted (about 3 minutes). Add the eggs, one at a time, and the vanilla, and beat again until well-combined. Next, add the chocolate and the brewed coffee, beating to combine after each addition. Finally, with the mixer on low, add the flour and cocoa powder mixture slowly. Beat briefly until just combined. The batter should be smooth and thickly pourable.
• Pour the batter into the prepared pan, and smooth the top with a wet spatula. Place in the center of the preheated oven and bake until a toothpick inserted in the center comes out with no more than a few moist crumbs attached (about 1 hour). Remove from the oven and allow to cool in the pan for 10 minutes before turning out onto a wire rack to cool completely.

Make the glaze.

• Place the chopped chocolate in a small, heat-safe bowl. Place the cream and vanilla in a small saucepan and bring to a simmer over medium-low heat. Pour the hot cream over the chopped chocolate and allow to sit until the chocolate begins to melt (about 1 minute). Mix until the chocolate is melted and smooth. Pour the glaze over the top of the cooled pound cake and spread into an even layer with a small offset spatula or large knife. Allow to sit at room temperature until the glaze is set. Slice thickly and serve.