Preheat the oven to 325°F. Spray a 9-inch round cake pan with cooking spray, line the bottom with a circle of parchment paper, and spray the parchment and sides of the pan.

Chop the 10 (1‑ounce) squares of semisweet chocolate if not already chopped.

In a medium saucepan over medium‑low heat, combine the 3/4 cup (12 tablespoons) unsalted butter, the chopped semisweet chocolate, and the 1/2 cup creamy peanut butter. Stir constantly until the mixture is completely melted and smooth. (Alternatively, melt in a microwave‑safe bowl in 30‑second intervals, stirring between each interval, until smooth.)

Remove the pan from heat. Whisk the 1 1/2 cups sugar into the warm chocolate mixture until fully incorporated, about 2 minutes. Let the mixture cool briefly (about 1–2 minutes) so it is warm but not hot.

Add the 6 egg yolks to the chocolate mixture one at a time, whisking well after each addition until each yolk is fully incorporated.

In a clean medium bowl, beat the 6 egg whites on high speed with a mixer until stiff peaks form. (Ensure no yolk is in the whites.)

Gently fold the beaten egg whites into the chocolate mixture: first fold in about one‑third of the whites to lighten the batter, then fold in the remaining whites in two additions until combined. Use gentle folding motions to preserve as much volume as possible; stop when no large streaks of white remain.

Pour the batter into the prepared pan and smooth the top with a spatula.

Bake in the preheated 325°F oven for 45–60 minutes, until the top is set and the center is slightly underdone (a gentle jiggle in the center is acceptable). Do not overbake.

Remove the souffle from the oven and cool on a rack for 1 hour. After it has cooled, refrigerate for at least 4 hours before serving. You may serve cold or warm (reheat briefly if desired).