½ lb. (2 sticks) unsalted butter, plus extra for greasing the dish
4 large eggs, at room temperature
2 cups sugar
¾ cup cocoa powder
½ cup all-purpose flour
1 vanilla bean, split lengthwise
step 1: Show Images
Preheat the oven to 325˚ F. Lightly butter a 2-quart oval baking dish. Melt the 2 sticks of butter and set aside to cool.
step 2: Show Images
In the bowl of an electric mixer fitted with the paddle attachment, combine the eggs and sugar. Beat together on medium-high speed until thick and light yellow in color. Meanwhile, combine the flour and cocoa powder in a medium bowl and whisk together until blended.
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When the eggs and sugar are finished mixing, scrape the seeds from the vanilla bean into the mixing bowl. Add the flour-cocoa powder mixture to the bowl as well. Mix on low speed just until combined. With the mixer still on low, slowly pour the melted butter and mix again just until combined.
step 4: Show Images
Pour the mixture into the prepared baking dish. Place the baking dish in a larger baking pan. Add very hot tap water to the outer baking pan to create a water bath, coming halfway up the side of the baking dish. Bake for 60 minutes. The center will appear very under-baked, that is the way the dessert should be. Allow to cool slightly before serving with ice cream.