Ingredients
12tbspunsalted butter,(1½ sticks) plus more for greasing the pan
6ozsemisweet chocolate,chopped
1¼cupsugar
5large eggs
½cupDutch-process cocoa powder
4large egg whites
⅛tspcream of tartar
¾cupsugar
Preparation
Set a rack in the middle of the oven and preheat to 350 degrees F. Generously butter a 9-inch springform pan.
In a large microwave-safe bowl, melt the butter in the microwave until foamy. Add the chopped chocolate and stir until completely melted and smooth. Add the sugar and whisk until well combined. Whisk in the eggs.
Whisk in the cocoa powder in 3 separate additions, using a folding motion at first so it doesn’t fly out of the bowl. Pour the batter into the prepared pan and bake for 35 to 40 min, or until the cake is set.
Bring ½-inch of water to a boil in a small saucepan, then lower the heat so that the water just simmers. Combine the egg whites, cream of tartar, and sugar in the bowl of an electric mixer.
Set the bowl over the pan of simmering water, making sure the bottom of the bowl does not touch the water. Whisk gently for about 3 minutes, until the egg whites are hot to the touch and the sugar is dissolved.
Remove the bowl from the pan and attach it to the stand mixer. Fit the mixer with the whisk attachment and whisk on medium speed for about 5 minutes until the meringue is cooled, glossy and stiff.
Set aside until the cake is done.
When the cake comes out of the oven, give the meringue a quick whisk, then pile it onto the hot cake, leaving a 1-inch border around the perimeter. Use a small spoon to swirl it into dramatic peaks.
Place the cake back into the oven for 10 to 12 minutes, until the peaks are lightly browned. Let the cake cool on a rack, then run a sharp knife around the edges to loosen any meringue that may have stuck to the sides.
Carefully remove the sides of the springform pan. Transfer the cake to a platter and serve at room temperature.
