Preheat your oven to 425°F (220°C). Grease four ramekins with butter and lightly dust with flour to prevent sticking.
In a medium saucepan over low heat, melt the butter and chocolate chips together, stirring continuously until smooth. Remove from heat and let cool slightly.
In a large mixing bowl, whisk together the eggs, egg yolks, and granulated sugar until pale and fluffy.
Slowly mix the melted chocolate mixture into the egg mixture, adding the vanilla extract and salt. Stir until well combined.
Gently fold in the flour, being careful not to overmix.
Divide half of the batter evenly among the prepared ramekins.
Add a tablespoon of creamy peanut butter into the center of each ramekin, then cover with the remaining batter.
Place the filled ramekins on a baking sheet and bake in the preheated oven for 12-14 minutes, until the edges are set but the center is still soft.
Remove from the oven and allow to cool for 1-2 minutes before carefully inverting each ramekin onto a plate.
Dust the tops with powdered sugar if desired, and garnish with fresh raspberries.