Preparation

• Position a rack in the lower third of the oven and heat the oven to 350 F. Grease the bottom of an 8×2- or 9×2-inch round cake pan or line it with parchment.
• In a small bowl, whisk the flour, cocoa powder, baking soda, and salt. Sift only if the cocoa remains lumpy after whisking. In a large bowl, combine the melted butter and brown sugar with a wooden spoon or rubber spatula. 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. Scrape the batter into the prepared pan. Bake until a toothpick inserted in the center comes out clean, about 30 minutes for a 9-inch pan; 35 to 40 min. for an 8-inch pan. Let cool in the pan on a rack for 10 min. Run a thin knife around the edge and invert the cake (peel off the parchment if necessary). Invert it again onto the rack and let cool completely.
• Once cool, set the rack over a baking sheet or foil. Pour the warm ganache over the cake and use an icing spatula to spread it over the top of the cake and down the sides. Let set for about an hour before serving.