Make ganache. Put the chocolate in a medium heatproof bowl. In a saucepan or via the microwave, heat cream to a simmer.

Pour the hot cream over the chocolate and whisk gently until the chocolate is completely melted and smooth.

Add sugar and whisk to combine. Set aside and let cool enough so it doesn't all run off the cake when you glaze.

Preheat the oven to 350º. Grease the bottom of an 8-inch round cake pan or line it with parchment.

In a small bowl, whisk the flour, baking soda, and salt. Sift the cocoa into the dry ingredients and whisk to combine.

In a large bowl, combine the melted butter and brown sugar with a wooden spoon.

Add the eggs and vanilla; stir until well blended.

Add the flour mixture all at once and stir just until all the flour is moistened.

Pour the hot water over the batter; stir just until it’s incorporated and the batter is smooth. Pour the batter into the prepared pan.

Bake for about 35 to 40 minutes or till a toothpick inserted into the center of the cake comes out clean.

Cool on a rack for 10 minutes, then run a knife around the edge of the cake and remove from the pan to finish cooling on the rack, removing parchment if used.

Once cool, set the rack over a baking sheet or foil. Pour the ganache over the cake and use an offset spatula to spread it over the top of the cake and down the sides.

Let set for about an hour before serving.