01 -
Preheat the oven to 350°F. Grease a 9-inch springform pan and line the bottom with parchment. Set the pan on a rimmed baking sheet.
02 -
Melt the butter with 1 1/2 cups of the chocolate chips in a heatproof bowl, using 30-second microwave bursts or a double boiler. Stir until smooth, then cool for 5 minutes.
03 -
In a large bowl, beat the eggs, sugar, and vanilla on medium-high speed for 2-3 minutes, until pale, thick, and slightly foamy.
04 -
Beat in the cooled melted chocolate mixture. Fold in the flour, cocoa powder, baking powder, and salt until just combined, then fold in the remaining 1 cup chocolate chips.
05 -
Spread the batter into the prepared pan. Bake for 36-40 minutes, until the top is puffed and crackly and a tester near the center comes out with moist crumbs.
06 -
Cool in the pan for at least 45 minutes. Run a knife around the edge, release the springform ring, and cut into wedges.
07 -
Drizzle each slice with warm hot fudge sauce. Add ice cream, whipped cream, or a small pinch of flaky salt if desired.