Preheat your oven to 325°F. Line a standard 12-cup muffin tin with greaseproof liners and set it aside.

Place the chopped chocolate in a small, microwave-safe bowl, and microwave on 60% power for 1 minute. Remove and stir until melted and smooth. If necessary, microwave again for 30 seconds on 60% power and stir until smooth and glossy. Set aside to cool briefly.

In a large bowl, place the flour, xanthan gum, cocoa powder, baking powder, baking soda, salt, and granulated sugar, and whisk to combine well.

Add the butter, sour cream, eggs, and vanilla, and then the melted chocolate, and mix until just combined. The batter should be relatively light and fluffy.

Fill the prepared muffin cups full, smoothing the tops with wet fingertips.

Place in the center of the preheated oven and bake, rotating once, just until a toothpick inserted in the center comes out clean (about 22 minutes).

Allow the cupcakes to cool for 10 minutes in the pan before transferring them to a wire rack to cool completely.

Place the chopped chocolate in a small heat-safe bowl or measuring cup with a wide open mouth.

Heat the cream until simmering in the microwave or in a small saucepan over low heat, and pour the hot cream over the chopped chocolate.

Allow the ingredients to sit undisturbed for at least 5 minutes to allow the chocolate to begin to melt. Mix until melted, smooth, and glossy. Allow the glaze to sit until it begins to thicken.

Dip the top of each cooled cupcake in the glaze, allow excess glaze to drip off, and place the cupcake, right side up, on a wire rack or parchment lined baking sheet to sit until the glaze is set (about 30 minutes).

You can speed up the process by placing the glazed cupcake in the refrigerator for a few minutes.