Preheat oven to 325°
Prepare a cake pan so it is prepared when the torte batter is ready to pour. Cut a round out of parchment to cover the bottom of the pan Cut strips of parchment to cover the inside of the pan sides. Spray the pan with non stick spray. Place the round in the bottom of the pan. Place the strips around the inside to cover overlapping a couple of inches Spray the parchment on the side that overlaps so it sticks to the other parchment. Spray the inside of the parchment lining the pan. In a bain marie, combine the butter and chocolate, heat over medium low heat to melt the butter and chocolate.
In a mixer, whip the egg whites to full volume stiff peaks. Careful not to over whip. Reserve the egg whites, in a bowl, in the refrigerator until needed.
In a mixer with a clean bowl, combine the egg yolks and sugar, whip to full volume.
Drizzle in the chocolate/butter mixture into the mixing bowl with the eggs and sugar. Slowly drizzle in the chocolate/butter to allow it to incorporate as the mixer is running on a low to medium speed.
Once combined remove the bowl from the mixer and scrape the sides and bottom to ensure the batter is incorporated.
Fold in the reserved egg whites in three stages. The egg whites do not have to be fully broken down. Remember, the egg whites is what allows this torte to rise. Leaving some bits of visible egg whites is good.
Pour the batter into the prepared cake pan. Level the top with a spatula.
Bake on a sheet pan with 2-3 cups of water on the sheet pan. This water bath allows for an even bake of the torte without burning the torte.
Bake for 40 minutes. The torte should be pulling away from the side of the pan and the top maybe cracking.
Leave the torte in the pan to cool to room temperature. Refrigerate after it comes to room temperature. Once at room temperature, refrigerate overnight to allow it to set further.