Preheat the oven to 400º.
Spray the bottom and sides of a 9-inch springform pan with non-stick cooking spray or cooking spray with flour.
Line the bottom with a round of parchment and grease the top.
Wrap the sides in 2 layers of aluminum foil and then place in a roasting pan and set aside.
As an alternative, you can place your pan in a cheesecake moat which I love!!
Melt the chocolate and the butter until smooth.
Add vanilla.
Crack eggs into the bowl of an electric mixer and beat on high speed until light and tripled in volume, 4 to 5 minutes.
Add ¼ of the whipped eggs to the chocolate mixture.
Fold in the eggs thoroughly to lighten the chocolate mixture.
Gently fold the remaining eggs into the chocolate mixture.
Transfer immediately to the prepared springform pan.
Pour hot water into the roasting pan until it reaches halfway up the sides of the springform.
Bake for 17-18 minutes; the center will be jiggly when removed from the oven. Remove from the water bath and cool to room temperature. Remove the foil. Run a knife around the perimeter of the pan.