Preheat the oven to 300.

Line the wells of a standard-sized muffin tin with paper liners.

Put the semisweet chocolate in a medium bowl with the hot coffee. Let stand, stirring occasionally, until the chocolate is melted and the mixture is smooth and opaque.

Meanwhile, in another medium bowl, whisk together the sugar, flour, cocoa powder, baking soda, baking powder and salt.

In the bowl of a stand mixer beat the egg on medium speed until it is pale yellow, about 1 minute. Add the oil, yogurt, and vanilla, beating well.

Gradually pour in the melted chocolate mixture, and beat to thoroughly combine.

Add the dry ingredients all at once, and beat on low speed until the batter is just combined.

Using a rubber spatula, scrape down the sides of the bowl and briefly stir to make sure that all the dry ingredients are absorbed.

Spoon the batter into the wells of the muffin tin, making sure that it is evenly distributed.

Bake for 20-25 minutes, or until a toothpick inserted in the center of one comes out clean.

Transfer the pan to a wire rack and cool for 20 minutes before---carefully, they're tender!--removing the cupcakes.

Allow them to cool completely before glazing.

To make the glaze, melt the bittersweet chocolate in a metal or glass bowl set over a pan of gently simmering water.

Stir frequently to prevent scorching.

When the chocolate is comletely smooth, it's ready.

Working with one cupcake at a time, spoon a heaping teaspoonful of melted chocolate on top. Tilt and rotate the cupcake to coax the chocolate out to the edge.

Alternatively, use a knife or icing spatula to spread the chocolate.

The top of the cupcake should be entirely covered with a thin layer of chocolate.

Spoon on more chocolate as needed.

Set the cupcakes aside at room temperature until ready to serve, at least an hour. The chocolateglaze will firm up a bit and become matte. You can, of course serve them with the chocolate still warm and soft if you just can't possibly wait any longer!