Preheat the oven to 425°F (220°C). Grease four ramekins (6 oz size) with butter and dust with cocoa powder, tapping out any excess.
In a heatproof bowl, melt the chocolate chips and butter together in a microwave or over a double boiler, stirring until smooth. Let it cool slightly.
In another bowl, whisk together the eggs, egg yolks, granulated sugar, and vanilla extract until combined and slightly frothy.
Gradually fold the melted chocolate mixture into the egg mixture until well combined.
Sift the flour and salt directly into the batter, folding gently until just mixed. Be careful not to over-mix.
Divide the batter evenly among the prepared ramekins. Add about 2-3 fresh raspberries into the center of each ramekin, pressing them slightly into the batter.
Place the ramekins on a baking sheet and bake in the preheated oven for 12-14 minutes, until the edges are firm but the center is still soft.
Remove from the oven and let them sit for a minute. Carefully run a knife around the edges of each cake, then invert them onto individual plates.
Dust the tops with powdered sugar and garnish with fresh mint leaves if desired.
Notes
Serve warm for the best experience, and consider adding a scoop of vanilla ice cream.