Preheat your oven to 425°F (220°C). Grease four 6-ounce ramekins with nonstick spray or butter, then dust with cocoa powder.
In a small bowl, mix peanut butter, 2 tablespoons of butter, and powdered sugar until smooth. Divide into 4 balls and place in the freezer.
Melt the chopped chocolate and 1/2 cup butter together in a heatproof bowl over simmering water (double boiler method). Stir until smooth.
Remove from heat and let cool slightly. Whisk in the eggs, egg yolks, sugar, and salt until combined.
Fold in the flour just until incorporated.
Divide the batter evenly between prepared ramekins. Press a frozen peanut butter ball into the center of each and cover with batter.
Place ramekins on a baking sheet and bake for 12–14 minutes, or until the edges are set but centers are soft.
Let rest for 1 minute, then run a knife around the edges to loosen and carefully invert onto plates.
Serve warm for maximum lava goodness.