Bittersweet chocolate pudding

In a medium saucepan, whisk together the cornstarch, cocoa powder, sugar salt, and salt

In a separate bowl, combine the milk and egg

Gradually pour the milk mixture into the saucepan, whisking until thoroughly mixed

Heat the mixture, stirring constantly, over medium heat until it boils

Cook for 1 minute, then remove from heat

Stir in butter and vanilla extract

Pour the pudding into the suitable molds rinsed with cold water (the pudding can be taken out more easily)