This rich and indulgent one-pot recipe makes a large-scale chocolate lava cake using a Dutch oven, perfect for serving a crowd without the hassle of individual portions.
Preheat oven to 325°F and position the rack in the middle. Melt butter, chocolate, and ⅔ cup cocoa powder in a 5-quart Dutch oven over low heat, stirring frequently until smooth (2 to 4 minutes). Remove from heat and let cool slightly.
In a separate bowl, mix brown sugar, ⅔ cup granulated sugar, and remaining ⅔ cup cocoa powder, breaking up any lumps.
Whisk milk, vanilla, egg yolks, baking powder, salt, and the remaining 1 ⅓ cups granulated sugar into the cooled chocolate mixture. Stir in flour until just combined. Sprinkle the brown sugar mixture evenly over the batter, covering the entire surface. Pour boiling water gently over the top without stirring.
Scrape down any batter from the sides of the Dutch oven, then transfer to the oven. Bake uncovered until the cake begins to pull away from the sides and the top is just firm to the touch, about 1 ¼ to 1 ½ hours, rotating the pot halfway through baking.
Remove the Dutch oven from the oven and transfer it to a wire rack. Let the cake cool for 15 minutes before serving. Serve warm with whipped cream or ice cream.